After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part"), the trick to set duty > period to properly shut down TCU2 channels did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org --- drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip *jz, + unsigned int hwpwm, + enum pwm_polarity polarity) +{ + unsigned int value = 0; + + if (polarity == PWM_POLARITY_INVERSED) + value = TCU_TCSR_PWM_INITL_HIGH; + + regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm), + TCU_TCSR_PWM_INITL_HIGH, value); +} + static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty; + enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
+ /* Restore regular polarity before disabling the channel. */ + jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity); + jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /* - * Set polarity. - * - * The PWM starts in inactive state until the internal timer reaches the - * duty value, then becomes active until the timer reaches the period - * value. In theory, we should then use (period - duty) as the real duty - * value, as a high duty value would otherwise result in the PWM pin - * being inactive most of the time. - * - * Here, we don't do that, and instead invert the polarity of the PWM - * when it is active. This trick makes the PWM start with its active - * state instead of its inactive state. - */ - if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled) - regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), - TCU_TCSR_PWM_INITL_HIGH, 0); - else - regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), - TCU_TCSR_PWM_INITL_HIGH, - TCU_TCSR_PWM_INITL_HIGH); - - if (state->enabled) + if (state->enabled) { + /* + * Set polarity. + * + * The PWM starts in inactive state until the internal timer + * reaches the duty value, then becomes active until the timer + * reaches the period value. In theory, we should then use + * (period - duty) as the real duty value, as a high duty value + * would otherwise result in the PWM pin being inactive most of + * the time. + * + * Here, we don't do that, and instead invert the polarity of + * the PWM when it is active. This trick makes the PWM start + * with its active state instead of its inactive state. + */ + if (state->polarity == PWM_POLARITY_NORMAL) + polarity = PWM_POLARITY_INVERSED; + else + polarity = PWM_POLARITY_NORMAL; + + jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity); + jz4740_pwm_enable(chip, pwm); + }
return 0; }
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part"), the trick to set duty > period to properly shut down TCU2 channels did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; } +static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip *jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel. */
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity);
Does this introduce a glitch?
jz4740_pwm_disable(chip, pwm); err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internal timer reaches the* duty value, then becomes active until the timer reaches the period* value. In theory, we should then use (period - duty) as the real duty* value, as a high duty value would otherwise result in the PWM pin* being inactive most of the time.** Here, we don't do that, and instead invert the polarity of the PWM* when it is active. This trick makes the PWM start with its active* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internal timer* reaches the duty value, then becomes active until the timer* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high duty value* would otherwise result in the PWM pin being inactive most of* the time.** Here, we don't do that, and instead invert the polarity of* the PWM when it is active. This trick makes the PWM start* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Best regards Uwe
Le mar. 25 oct. 2022 à 08:44:10 +0200, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part"), the trick to set duty > period to properly shut down TCU2 channels did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip *jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel. */
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity);
Does this introduce a glitch?
Maybe. But the PWM is shut down before finishing its period anyway, so there was already a glitch.
jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internal timerreaches the
* duty value, then becomes active until the timer reaches theperiod
* value. In theory, we should then use (period - duty) as thereal duty
* value, as a high duty value would otherwise result in the PWMpin
* being inactive most of the time.** Here, we don't do that, and instead invert the polarity of thePWM
* when it is active. This trick makes the PWM start with itsactive
* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internal timer* reaches the duty value, then becomes active until the timer* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high duty value* would otherwise result in the PWM pin being inactive most of* the time.** Here, we don't do that, and instead invert the polarity of* the PWM when it is active. This trick makes the PWM start* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
-Paul
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Le mar. 25 oct. 2022 à 08:44:10 +0200, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part"), the trick to set duty > period to properly shut down TCU2 channels did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip *jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel. */
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity);
Does this introduce a glitch?
Maybe. But the PWM is shut down before finishing its period anyway, so there was already a glitch.
jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internal timerreaches the
* duty value, then becomes active until the timer reaches theperiod
* value. In theory, we should then use (period - duty) as thereal duty
* value, as a high duty value would otherwise result in the PWMpin
* being inactive most of the time.** Here, we don't do that, and instead invert the polarity of thePWM
* when it is active. This trick makes the PWM start with itsactive
* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internal timer* reaches the duty value, then becomes active until the timer* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high duty value* would otherwise result in the PWM pin being inactive most of* the time.** Here, we don't do that, and instead invert the polarity of* the PWM when it is active. This trick makes the PWM start* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Best regards Uwe
On Mon, Nov 28, 2022 at 03:39:11PM +0100, Uwe Kleine-König wrote:
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Le mar. 25 oct. 2022 à 08:44:10 +0200, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part"), the trick to set duty > period to properly shut down TCU2 channels did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the active part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip *jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel. */
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity);
Does this introduce a glitch?
Maybe. But the PWM is shut down before finishing its period anyway, so there was already a glitch.
jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internal timerreaches the
* duty value, then becomes active until the timer reaches theperiod
* value. In theory, we should then use (period - duty) as thereal duty
* value, as a high duty value would otherwise result in the PWMpin
* being inactive most of the time.** Here, we don't do that, and instead invert the polarity of thePWM
* when it is active. This trick makes the PWM start with itsactive
* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^ state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internal timer* reaches the duty value, then becomes active until the timer* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high duty value* would otherwise result in the PWM pin being inactive most of* the time.** Here, we don't do that, and instead invert the polarity of* the PWM when it is active. This trick makes the PWM start* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Depending on your hardware capabilities you may also be able to use pinctrl to configure the pin to behave properly when the PWM is disabled. Not all hardware can do that, though.
Thierry
Hi Thierry,
Le mar. 29 nov. 2022 à 13:16:05 +0100, Thierry Reding thierry.reding@gmail.com a écrit :
On Mon, Nov 28, 2022 at 03:39:11PM +0100, Uwe Kleine-König wrote:
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Le mar. 25 oct. 2022 à 08:44:10 +0200, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with
the
active part"), the trick to set duty > period to properly shut down TCU2
channels
did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the
active
part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c
b/drivers/pwm/pwm-jz4740.c
index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct
pwm_chip
*chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip
*jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct
pwm_chip
*chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct
pwm_chip
*chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel.
*/
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm,
state->polarity);
Does this introduce a glitch?
Maybe. But the PWM is shut down before finishing its period
anyway, so there
was already a glitch.
jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct
pwm_chip
*chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internaltimer
reaches the
* duty value, then becomes active until the timer reachesthe
period
* value. In theory, we should then use (period - duty) asthe
real duty
* value, as a high duty value would otherwise result inthe PWM
pin
* being inactive most of the time.** Here, we don't do that, and instead invert the polarityof the
PWM
* when it is active. This trick makes the PWM start withits
active
* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^
state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internaltimer
* reaches the duty value, then becomes active until thetimer
* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high dutyvalue
* would otherwise result in the PWM pin being inactivemost of
* the time.** Here, we don't do that, and instead invert thepolarity of
* the PWM when it is active. This trick makes the PWMstart
* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about
the pin
state. So it would be ok (but admittedly not great) to simplify
the
driver and accept that the pinstate is active while the PWM is
off.
IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they
should
not disable it.
Completely disagree. I absolutely do not want the backlight to go
full
bright mode when the PWM pin is disabled. And disabling the
backlight is a
thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Depending on your hardware capabilities you may also be able to use pinctrl to configure the pin to behave properly when the PWM is disabled. Not all hardware can do that, though.
Been there, done that. It got refused. https://lkml.org/lkml/2019/5/22/607
Cheers, -Paul
Hi Uwe,
Le lun. 28 nov. 2022 à 15:39:11 +0100, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Le mar. 25 oct. 2022 à 08:44:10 +0200, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
On Mon, Oct 24, 2022 at 09:52:10PM +0100, Paul Cercueil wrote:
After commit a020f22a4ff5 ("pwm: jz4740: Make PWM start with
the
active part"), the trick to set duty > period to properly shut down TCU2
channels
did not work anymore, because of the polarity inversion.
Address this issue by restoring the proper polarity before disabling the channels.
Fixes: a020f22a4ff5 ("pwm: jz4740: Make PWM start with the
active
part") Signed-off-by: Paul Cercueil paul@crapouillou.net Cc: stable@vger.kernel.org
drivers/pwm/pwm-jz4740.c | 62 ++++++++++++++++++++++++++-------------- 1 file changed, 40 insertions(+), 22 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c
b/drivers/pwm/pwm-jz4740.c
index 228eb104bf1e..65462a0052af 100644 --- a/drivers/pwm/pwm-jz4740.c +++ b/drivers/pwm/pwm-jz4740.c @@ -97,6 +97,19 @@ static int jz4740_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm) return 0; }
+static void jz4740_pwm_set_polarity(struct jz4740_pwm_chip
*jz,
unsigned int hwpwm,enum pwm_polarity polarity)+{
- unsigned int value = 0;
- if (polarity == PWM_POLARITY_INVERSED)
value = TCU_TCSR_PWM_INITL_HIGH;- regmap_update_bits(jz->map, TCU_REG_TCSRc(hwpwm),
TCU_TCSR_PWM_INITL_HIGH, value);+}
static void jz4740_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm) { struct jz4740_pwm_chip *jz = to_jz4740(chip); @@ -130,6 +143,7 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long tmp = 0xffffull * NSEC_PER_SEC; struct clk *clk = pwm_get_chip_data(pwm); unsigned long period, duty;
- enum pwm_polarity polarity; long rate; int err;
@@ -169,6 +183,9 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (duty >= period) duty = period - 1;
- /* Restore regular polarity before disabling the channel. */
- jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, state->polarity);
Does this introduce a glitch?
Maybe. But the PWM is shut down before finishing its period anyway, so there was already a glitch.
jz4740_pwm_disable(chip, pwm);
err = clk_set_rate(clk, rate); @@ -190,29 +207,30 @@ static int jz4740_pwm_apply(struct
pwm_chip
*chip, struct pwm_device *pwm, regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm), TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
- /*
* Set polarity.** The PWM starts in inactive state until the internal timerreaches the
* duty value, then becomes active until the timer reachesthe
period
* value. In theory, we should then use (period - duty) asthe
real duty
* value, as a high duty value would otherwise result in thePWM
pin
* being inactive most of the time.** Here, we don't do that, and instead invert the polarityof the
PWM
* when it is active. This trick makes the PWM start with itsactive
* state instead of its inactive state.*/- if ((state->polarity == PWM_POLARITY_NORMAL) ^
state->enabled)
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH, 0);- else
regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),TCU_TCSR_PWM_INITL_HIGH,TCU_TCSR_PWM_INITL_HIGH);- if (state->enabled)
- if (state->enabled) {
/** Set polarity.** The PWM starts in inactive state until the internal timer* reaches the duty value, then becomes active until thetimer
* reaches the period value. In theory, we should then use* (period - duty) as the real duty value, as a high dutyvalue
* would otherwise result in the PWM pin being inactivemost of
* the time.** Here, we don't do that, and instead invert the polarityof
* the PWM when it is active. This trick makes the PWM start* with its active state instead of its inactive state.*/if (state->polarity == PWM_POLARITY_NORMAL)polarity = PWM_POLARITY_INVERSED;elsepolarity = PWM_POLARITY_NORMAL;jz4740_pwm_set_polarity(jz4740, pwm->hwpwm, polarity);- jz4740_pwm_enable(chip, pwm);
- }
Note that for disabled PWMs there is no official guaranty about
the pin
state. So it would be ok (but admittedly not great) to simplify
the
driver and accept that the pinstate is active while the PWM is
off.
IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they
should
not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Well that sounds pretty stupid to me; why doesn't the PWM subsystem enforce that the pins must be driven to their inactive level when the PWM function is disabled? Then for such hardware you describe, the corresponding PWM driver could itself apply a duty_cycle = 0 if that's what it takes to get an inactive state.
Cheers, -Paul
Hello Paul,
On Tue, Nov 29, 2022 at 12:25:56PM +0000, Paul Cercueil wrote:
Hi Uwe,
Le lun. 28 nov. 2022 à 15:39:11 +0100, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Well that sounds pretty stupid to me; why doesn't the PWM subsystem enforce that the pins must be driven to their inactive level when the PWM function is disabled?
Then for such hardware you describe, the corresponding PWM driver could itself apply a duty_cycle = 0 if that's what it takes to get an inactive state.
Let's assume we claim that on disable the pin is driven to the inactive level.
The (bad) effect is that for a use case where the pin state doesn't matter (e.g. a backlight where the power regulator is off), the PWM keeps running even though it could be disabled and so save some power.
So to make this use case properly supported, we need another flag in struct pwm_state that allows the consumer to tell the lowlevel driver that it's ok to disable the hardware even with the output being UB. Let's call this new flag "spam" and the pin is allowed to do whatever it wants with .spam = false.
After that you can realize that applying any state with:
.duty_cycle = A, .period = B, .polarity = C, .enabled = false, .spam = true,
semantically (i.e. just looking at the output) has the same effect as
.duty_cycle = 0, .period = $something, .polarity = C, .enabled = true, .spam = true,
So having .enabled doesn't add to the expressiveness of pwm_apply(), because you can specify any configuration without having to resort to .enabled = false. So the enabled member of struct pwm_state can be dropped.
Then we end up with the exact scenario we have now, just that the flag that specifies if the output should be held in the inactive state has a bad name.
Best regards Uwe
Le mardi 29 novembre 2022 à 17:24 +0100, Uwe Kleine-König a écrit :
Hello Paul,
On Tue, Nov 29, 2022 at 12:25:56PM +0000, Paul Cercueil wrote:
Hi Uwe,
Le lun. 28 nov. 2022 à 15:39:11 +0100, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Well that sounds pretty stupid to me; why doesn't the PWM subsystem enforce that the pins must be driven to their inactive level when the PWM function is disabled?
Then for such hardware you describe, the corresponding PWM driver could itself apply a duty_cycle = 0 if that's what it takes to get an inactive state.
Let's assume we claim that on disable the pin is driven to the inactive level.
The (bad) effect is that for a use case where the pin state doesn't matter (e.g. a backlight where the power regulator is off), the PWM keeps running even though it could be disabled and so save some power.
So to make this use case properly supported, we need another flag in struct pwm_state that allows the consumer to tell the lowlevel driver that it's ok to disable the hardware even with the output being UB. Let's call this new flag "spam" and the pin is allowed to do whatever it wants with .spam = false.
After that you can realize that applying any state with:
.duty_cycle = A, .period = B, .polarity = C, .enabled = false, .spam = true,
semantically (i.e. just looking at the output) has the same effect as
.duty_cycle = 0, .period = $something, .polarity = C, .enabled = true, .spam = true,
So having .enabled doesn't add to the expressiveness of pwm_apply(), because you can specify any configuration without having to resort to .enabled = false. So the enabled member of struct pwm_state can be dropped.
Then we end up with the exact scenario we have now, just that the flag that specifies if the output should be held in the inactive state has a bad name.
If I follow you, then it means that the PWM backlight driver pwm_bl.c should set state.enabled=true in pwm_backlight_power_off() to make sure that the pin is inactive?
-Paul
On Tue, Nov 29, 2022 at 04:58:28PM +0000, Paul Cercueil wrote:
Le mardi 29 novembre 2022 à 17:24 +0100, Uwe Kleine-König a écrit :
Hello Paul,
On Tue, Nov 29, 2022 at 12:25:56PM +0000, Paul Cercueil wrote:
Hi Uwe,
Le lun. 28 nov. 2022 à 15:39:11 +0100, Uwe Kleine-König u.kleine-koenig@pengutronix.de a écrit :
Hello,
On Tue, Oct 25, 2022 at 11:10:46AM +0100, Paul Cercueil wrote:
Note that for disabled PWMs there is no official guaranty about the pin state. So it would be ok (but admittedly not great) to simplify the driver and accept that the pinstate is active while the PWM is off. IMHO this is also better than a glitch.
If a consumer wants the PWM to be in its inactive state, they should not disable it.
Completely disagree. I absolutely do not want the backlight to go full bright mode when the PWM pin is disabled. And disabling the backlight is a thing (for screen blanking and during mode changes).
For some hardwares there is no pretty choice. So the gist is: If the backlight driver wants to ensure that the PWM pin is driven to its inactive level, it should use:
pwm_apply(pwm, { .period = ..., .duty_cycle = 0, .enabled = true });
and better not
pwm_apply(pwm, { ..., .enabled = false });
Well that sounds pretty stupid to me; why doesn't the PWM subsystem enforce that the pins must be driven to their inactive level when the PWM function is disabled?
Then for such hardware you describe, the corresponding PWM driver could itself apply a duty_cycle = 0 if that's what it takes to get an inactive state.
Let's assume we claim that on disable the pin is driven to the inactive level.
The (bad) effect is that for a use case where the pin state doesn't matter (e.g. a backlight where the power regulator is off), the PWM keeps running even though it could be disabled and so save some power.
So to make this use case properly supported, we need another flag in struct pwm_state that allows the consumer to tell the lowlevel driver that it's ok to disable the hardware even with the output being UB. Let's call this new flag "spam" and the pin is allowed to do whatever it wants with .spam = false.
After that you can realize that applying any state with:
.duty_cycle = A, .period = B, .polarity = C, .enabled = false, .spam = true,
semantically (i.e. just looking at the output) has the same effect as
.duty_cycle = 0, .period = $something, .polarity = C, .enabled = true, .spam = true,
So having .enabled doesn't add to the expressiveness of pwm_apply(), because you can specify any configuration without having to resort to .enabled = false. So the enabled member of struct pwm_state can be dropped.
Then we end up with the exact scenario we have now, just that the flag that specifies if the output should be held in the inactive state has a bad name.
If I follow you, then it means that the PWM backlight driver pwm_bl.c should set state.enabled=true in pwm_backlight_power_off() to make sure that the pin is inactive?
Correct, that's the only way to ensure that the pinlevel stays at the intended level.
And lowlevel PWM drivers can be improved to disable the hardware when they are asked for .duty_cycle = 0 (maybe under some additional conditions).
Best regards Uwe
linux-stable-mirror@lists.linaro.org
-
Paul Cercueil -
Thierry Reding -
Uwe Kleine-König