From: Andrew Jeffery andrew@aj.id.au
[ Upstream commit 52ca7d0f7bdad832b291ed979146443533ee79c0 ]
The PCA9552 lines can be used either for driving LEDs or as GPIOs. The manual states that for LEDs, the operation is open-drain:
The LSn LED select registers determine the source of the LED data.
00 = output is set LOW (LED on) 01 = output is set high-impedance (LED off; default) 10 = output blinks at PWM0 rate 11 = output blinks at PWM1 rate
For GPIOs it suggests a pull-up so that the open-case drives the line high:
For use as output, connect external pull-up resistor to the pin and size it according to the DC recommended operating characteristics. LED output pin is HIGH when the output is programmed as high-impedance, and LOW when the output is programmed LOW through the ‘LED selector’ register. The output can be pulse-width controlled when PWM0 or PWM1 are used.
Now, I have a hardware design that uses the LED controller to control LEDs. However, for $reasons, we're using the leds-gpio driver to drive the them. The reasons are here are a tangent but lead to the discovery of the inversion, which manifested as the LEDs being set to full brightness at boot when we expected them to be off.
As we're driving the LEDs through leds-gpio, this means wending our way through the gpiochip abstractions. So with that in mind we need to describe an active-low GPIO configuration to drive the LEDs as though they were GPIOs.
The set() gpiochip callback in leds-pca955x does the following:
... if (val) pca955x_led_set(&led->led_cdev, LED_FULL); else pca955x_led_set(&led->led_cdev, LED_OFF); ...
Where LED_FULL = 255. pca955x_led_set() in turn does:
... switch (value) { case LED_FULL: ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_LED_ON); break; ...
Where PCA955X_LS_LED_ON is defined as:
#define PCA955X_LS_LED_ON 0x0 /* Output LOW */
So here we have some type confusion: We've crossed domains from GPIO behaviour to LED behaviour without accounting for possible inversions in the process.
Stepping back to leds-gpio for a moment, during probe() we call create_gpio_led(), which eventually executes:
if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP) { state = gpiod_get_value_cansleep(led_dat->gpiod); if (state < 0) return state; } else { state = (template->default_state == LEDS_GPIO_DEFSTATE_ON); } ... ret = gpiod_direction_output(led_dat->gpiod, state);
In the devicetree the GPIO is annotated as active-low, and gpiod_get_value_cansleep() handles this for us:
int gpiod_get_value_cansleep(const struct gpio_desc *desc) { int value;
might_sleep_if(extra_checks); VALIDATE_DESC(desc); value = _gpiod_get_raw_value(desc); if (value < 0) return value;
if (test_bit(FLAG_ACTIVE_LOW, &desc->flags)) value = !value;
return value; }
_gpiod_get_raw_value() in turn calls through the get() callback for the gpiochip implementation, so returning to our get() implementation in leds-pca955x we find we extract the raw value from hardware:
static int pca955x_gpio_get_value(struct gpio_chip *gc, unsigned int offset) { struct pca955x *pca955x = gpiochip_get_data(gc); struct pca955x_led *led = &pca955x->leds[offset]; u8 reg = pca955x_read_input(pca955x->client, led->led_num / 8);
return !!(reg & (1 << (led->led_num % 8))); }
This behaviour is not symmetric with that of set(), where the val is inverted by the driver.
Closing the loop on the GPIO_ACTIVE_LOW inversions, gpiod_direction_output(), like gpiod_get_value_cansleep(), handles it for us:
int gpiod_direction_output(struct gpio_desc *desc, int value) { VALIDATE_DESC(desc); if (test_bit(FLAG_ACTIVE_LOW, &desc->flags)) value = !value; else value = !!value; return _gpiod_direction_output_raw(desc, value); }
All-in-all, with a value of 'keep' for default-state property in a leds-gpio child node, the current state of the hardware will in-fact be inverted; precisely the opposite of what was intended.
Rework leds-pca955x so that we avoid the incorrect inversion and clarify the semantics with respect to GPIO.
Signed-off-by: Andrew Jeffery andrew@aj.id.au Reviewed-by: Cédric Le Goater clg@kaod.org Tested-by: Joel Stanley joel@jms.id.au Tested-by: Matt Spinler mspinler@linux.vnet.ibm.com Signed-off-by: Jacek Anaszewski jacek.anaszewski@gmail.com Signed-off-by: Sasha Levin alexander.levin@verizon.com --- drivers/leds/leds-pca955x.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c index 905729191d3e..78183f90820e 100644 --- a/drivers/leds/leds-pca955x.c +++ b/drivers/leds/leds-pca955x.c @@ -61,6 +61,10 @@ #define PCA955X_LS_BLINK0 0x2 /* Blink at PWM0 rate */ #define PCA955X_LS_BLINK1 0x3 /* Blink at PWM1 rate */
+#define PCA955X_GPIO_INPUT LED_OFF +#define PCA955X_GPIO_HIGH LED_OFF +#define PCA955X_GPIO_LOW LED_FULL + enum pca955x_type { pca9550, pca9551, @@ -329,9 +333,9 @@ static int pca955x_set_value(struct gpio_chip *gc, unsigned int offset, struct pca955x_led *led = &pca955x->leds[offset];
if (val) - return pca955x_led_set(&led->led_cdev, LED_FULL); - else - return pca955x_led_set(&led->led_cdev, LED_OFF); + return pca955x_led_set(&led->led_cdev, PCA955X_GPIO_HIGH); + + return pca955x_led_set(&led->led_cdev, PCA955X_GPIO_LOW); }
static void pca955x_gpio_set_value(struct gpio_chip *gc, unsigned int offset, @@ -355,8 +359,11 @@ static int pca955x_gpio_get_value(struct gpio_chip *gc, unsigned int offset) static int pca955x_gpio_direction_input(struct gpio_chip *gc, unsigned int offset) { - /* To use as input ensure pin is not driven */ - return pca955x_set_value(gc, offset, 0); + struct pca955x *pca955x = gpiochip_get_data(gc); + struct pca955x_led *led = &pca955x->leds[offset]; + + /* To use as input ensure pin is not driven. */ + return pca955x_led_set(&led->led_cdev, PCA955X_GPIO_INPUT); }
static int pca955x_gpio_direction_output(struct gpio_chip *gc,