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

[Jacek Anaszewski <j.anaszewski@samsung.com>]

Hi Alvaro,

On 11/04/2015 04:46 PM, Álvaro Fernández Rojas wrote:
> 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.

BCM6328_LED_MODE_ON and BCM6328_LED_MODE_OFF should represent the values
that actually set the LED state according to the current logic.
Otherwise it will confuse people who will be analyzing this code.
We are interested in the logic as it is seen from this driver's
perspective and not GPIO perspective.

IMO the values should be swapped.

Best Regards,
Jacek Anaszewski

> 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;
>>>
>>
>>
>
>