Hi,

On 5/12/20 9:01 PM, Andy Shevchenko wrote:

On Tue, May 12, 2020 at 01:00:44PM +0200, Hans de Goede wrote:

...

Before commit cfc4c189bc70 ("pwm: Read initial hardware state at request time"), a driver's get_state callback would get called once per PWM from pwmchip_add().

pwm-lpss' runtime-pm code was relying on this, getting a runtime-pm ref for PWMs which are enabled at probe time from within its get_state callback, before enabling runtime-pm.

The change to calling get_state at request time causes a number of problems:

1. PWMs enabled at probe time may get runtime suspended before they are

requested, causing e.g. a LCD backlight controlled by the PWM to turn off.

2. When the request happens when the PWM has been runtime suspended, the

ctrl register will read all 1 / 0xffffffff, causing get_state to store bogus values in the pwm_state.

3. get_state was using an async pm_runtime_get() call, because it assumed

that runtime-pm has not been enabled yet. If shortly after the request an apply call is made, then the pwm_lpss_is_updating() check may trigger because the resume triggered by the pm_runtime_get() call is not complete yet, so the ctrl register still reads all 1 / 0xffffffff.

This commit fixes these issues by moving the initial pm_runtime_get() call for PWMs which are enabled at probe time to the pwm_lpss_probe() function; and by making get_state take a runtime-pm ref before reading the ctrl reg.

Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com

Thank you.

One thing to consider below.

...

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1828927 Fixes: cfc4c189bc70 ("pwm: Read initial hardware state at request time") Cc: stable@vger.kernel.org Signed-off-by: Hans de Goede hdegoede@redhat.com

---

drivers/pwm/pwm-lpss.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 75bbfe5f3bc2..9d965ffe66d1 100644 --- a/drivers/pwm/pwm-lpss.c +++ b/drivers/pwm/pwm-lpss.c @@ -158,7 +158,6 @@ static int pwm_lpss_apply(struct pwm_chip *chip, struct pwm_device *pwm, return 0; } -/* This function gets called once from pwmchip_add to get the initial state */ static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm, struct pwm_state *state) { @@ -167,6 +166,8 @@ static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm, unsigned long long base_unit, freq, on_time_div; u32 ctrl;

• pm_runtime_get_sync(chip->dev);
• base_unit_range = BIT(lpwm->info->base_unit_bits);

ctrl = pwm_lpss_read(pwm); @@ -187,8 +188,7 @@ static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm, state->polarity = PWM_POLARITY_NORMAL; state->enabled = !!(ctrl & PWM_ENABLE);

• if (state->enabled)

• pm_runtime_get(chip->dev);
  

• pm_runtime_put(chip->dev); }

static const struct pwm_ops pwm_lpss_ops = { @@ -202,7 +202,8 @@ struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev, struct resource *r, { struct pwm_lpss_chip *lpwm; unsigned long c;

• int ret;

• int i, ret;
• u32 ctrl;

if (WARN_ON(info->npwm > MAX_PWMS)) return ERR_PTR(-ENODEV); @@ -232,6 +233,12 @@ struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev, struct resource *r, return ERR_PTR(ret); }

• for (i = 0; i < lpwm->info->npwm; i++) {

...

• ctrl = pwm_lpss_read(&lpwm->chip.pwms[i]);
  

• if (ctrl & PWM_ENABLE)
  

I would create a helper for this as opposite to pwm_lpss_cond_enable(), something like pwm_lpss_is_enabled().

pwm_lpss_cond_enable() is used in multiple places, this check we only need once, so I would prefer to just keep it as is.

Regards,

Hans

...

• 	pm_runtime_get(dev);
  

• }
• return lpwm; } EXPORT_SYMBOL_GPL(pwm_lpss_probe);

-- 2.26.0