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SubjectRe: [PATCH] leds-bcm6328: Reuse bcm6328_led_set() instead of copying its functionality
Hi Simon,

Thanks for the patch. Generally this patch touches two
areas - replacement of redundant code with bcm6328_led_set,
and locking reorganization. These should be split into
two separate patches. Nonetheless, I've noticed some
issues in the code, please refer below.

On 10/29/2015 08:48 PM, Simon Arlott wrote:
> When ensuring a consistent initial LED state in bcm6328_led (as they may
> be blinking instead of on/off), the LED register is set using a copy of
> bcm6328_led_set(). To avoid further errors relating to active low handling,
> call this function directly instead.
>
> As bcm6328_led_set() expects to acquire the spinlock, narrow the locking
> to only cover reading of the current state. There is no need to hold the
> spinlock between reading the current value and setting it again because
> the LED device has not yet been registered.
>
> Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
> ---
> drivers/leds/leds-bcm6328.c | 14 +++++---------
> 1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/leds/leds-bcm6328.c b/drivers/leds/leds-bcm6328.c
> index c7ea5c6..db327bd 100644
> --- a/drivers/leds/leds-bcm6328.c
> +++ b/drivers/leds/leds-bcm6328.c
> @@ -264,7 +264,6 @@ static int bcm6328_led(struct device *dev, struct device_node *nc, u32 reg,
> unsigned long *blink_leds, unsigned long *blink_delay)
> {
> struct bcm6328_led *led;
> - unsigned long flags;
> const char *state;
> int rc;
>
> @@ -286,13 +285,12 @@ static int bcm6328_led(struct device *dev, struct device_node *nc, u32 reg,
> "linux,default-trigger",
> NULL);
>
> - spin_lock_irqsave(lock, flags);
> if (!of_property_read_string(nc, "default-state", &state)) {
> if (!strcmp(state, "on")) {
> led->cdev.brightness = LED_FULL;
> } else if (!strcmp(state, "keep")) {
> void __iomem *mode;
> - unsigned long val, shift;
> + unsigned long val, shift, flags;
>
> shift = bcm6328_pin2shift(led->pin);
> if (shift / 16)
> @@ -300,9 +298,12 @@ static int bcm6328_led(struct device *dev, struct device_node *nc, u32 reg,
> else
> mode = mem + BCM6328_REG_MODE_LO;
>
> + spin_lock_irqsave(lock, flags);
> val = bcm6328_led_read(mode) >>
> BCM6328_LED_SHIFT(shift % 16);
> val &= BCM6328_LED_MODE_MASK;
> + spin_unlock_irqrestore(lock, flags);
> +
> if ((led->active_low && val == BCM6328_LED_MODE_ON) ||
> (!led->active_low && val == BCM6328_LED_MODE_OFF))
> led->cdev.brightness = LED_FULL;
> @@ -315,12 +316,7 @@ static int bcm6328_led(struct device *dev, struct device_node *nc, u32 reg,
> led->cdev.brightness = LED_OFF;
> }
>
> - if ((led->active_low && led->cdev.brightness == LED_FULL) ||
> - (!led->active_low && led->cdev.brightness == LED_OFF))
> - bcm6328_led_mode(led, BCM6328_LED_MODE_ON);
> - else
> - bcm6328_led_mode(led, BCM6328_LED_MODE_OFF);

There are some problems with active_low mode here, I didn't recognize
earlier.

I'd expect that active_low implies reverse logic, i.e.:

LED_FULL -> bcm6328_led_mode(led, BCM6328_LED_MODE_OFF);
LED_OFF -> bcm6328_led_mode(led, BCM6328_LED_MODE_ON);

Let's take a look at bcm6328_led_set:

if ((led->active_low && value == LED_OFF) ||
(!led->active_low && value != LED_OFF))
bcm6328_led_mode(led, BCM6328_LED_MODE_OFF);
else
bcm6328_led_mode(led, BCM6328_LED_MODE_ON);

which, for active_low case, boils down to:

LED_FULL -> bcm6328_led_mode(led, BCM6328_LED_MODE_ON);
LED_OFF -> bcm6328_led_mode(led, BCM6328_LED_MODE_OFF);

and for !active_low case to:

LED_FULL -> bcm6328_led_mode(led, BCM6328_LED_MODE_OFF);
LED_OFF -> bcm6328_led_mode(led, BCM6328_LED_MODE_ON);

so, this is the other way round.

In bcm6328_led we have:

if ((led->active_low && val == BCM6328_LED_MODE_ON) ||
(!led->active_low && val == BCM6328_LED_MODE_OFF))
led->cdev.brightness = LED_FULL;
else
led->cdev.brightness = LED_OFF;

which, for active_low case, boils down to:

BCM6328_LED_MODE_ON -> led->cdev.brightness = LED_FULL
BCM6328_LED_MODE_OFF -> led->cdev.brightness = LED_OFF

and for !active_low case to:

BCM6328_LED_MODE_ON -> led->cdev.brightness = LED_OFF
BCM6328_LED_MODE_OFF -> led->cdev.brightness = LED_FULL

again, the other way round.

All this looks like active_low really means active high.
Correct me if I'm wrong.

Alvaro, Jonas, could you also help to clarify this discrepancy?


> - spin_unlock_irqrestore(lock, flags);
> + bcm6328_led_set(&led->cdev, led->cdev.brightness);
>
> led->cdev.brightness_set = bcm6328_led_set;
> led->cdev.blink_set = bcm6328_blink_set;
>


--
Best Regards,
Jacek Anaszewski


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