linux-kernel - Re: [PATCH 1/2 (v2)] leds-bcm6328: Reuse bcm6328_led_set() instead of copying its functionality

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Date:	Tue, 17 Nov 2015 09:15:05 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Simon Arlott <simon@...e.lp0.eu>
Cc:	Álvaro Fernández Rojas <noltari@...il.com>,
	Jonas Gorski <jogo@...nwrt.org>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 (v2)] leds-bcm6328: Reuse bcm6328_led_set() instead of
 copying its functionality

On 11/17/2015 09:06 AM, Jacek Anaszewski wrote:
> Hi Alvaro, Simon,
>
> On 11/17/2015 08:42 AM, Simon Arlott wrote:
>> On 16/11/15 21:33, Álvaro Fernández Rojas wrote:
>>> Still wrong, you are setting the led value after unlocking the spinlock.
>>
>> I have to unlock it because bcm6328_led_set() locks that spinlock.
>
> Commit message from the first version of the patch justified that
> properly. It should be preserved in the final patch:
>
> 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.

Hmm, if so, then spin_lock in bcm6328_led isn't needed at all, as it
is guaranteed that no concurrent process will be executing this
function.

>>> El 16/11/2015 a las 21:24, Simon Arlott escribió:
>>>> 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 an
>>>> inverted
>>>> copy of bcm6328_led_set(). To avoid further errors relating to
>>>> active low
>>>> handling, call this function directly instead.
>>>>
>>>> As bcm6328_led_set() acquires the same spinlock again when updating the
>>>> register, it is called after unlocking.
>>>>
>>>> Signed-off-by: Simon Arlott <simon@...e.lp0.eu>
>>>> ---
>>>>    drivers/leds/leds-bcm6328.c | 8 ++------
>>>>    1 file changed, 2 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/leds/leds-bcm6328.c b/drivers/leds/leds-bcm6328.c
>>>> index c7ea5c6..95d0cf9 100644
>>>> --- a/drivers/leds/leds-bcm6328.c
>>>> +++ b/drivers/leds/leds-bcm6328.c
>>>> @@ -314,14 +314,10 @@ static int bcm6328_led(struct device *dev,
>>>> struct device_node *nc, u32 reg,
>>>>        } else {
>>>>            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);
>>>>        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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