Re: [PATCH] leds-bcm6328: Reuse bcm6328_led_set() instead of copying its functionality

["Álvaro Fernández Rojas" <noltari@gmail.com>]

Hello Jacek,

BCM6328_LED_MODE_ON and BCM6328_LED_MODE_OFF values were extracted from 
Broadcom's GPL code, in which they assume leds are active low by default.
I can confirm the code is correct as it is right now, since those values 
match the active high / low values of the LEDs managed by GPIO instead 
of by using this driver.

Regards,
Álvaro.

El 04/11/2015 a las 16:41, Jacek Anaszewski escribió:
> 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;
>>
>
>