linux-kernel - Re: [PATCH/RFC v5 2/4] leds: implement sysfs interface locking mechanism

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Date:	Fri, 12 Sep 2014 08:45:03 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Bryan Wu <cooloney@...il.com>
Cc:	Linux LED Subsystem <linux-leds@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	b.zolnierkie@...sung.com, Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH/RFC v5 2/4] leds: implement sysfs interface locking
 mechanism

Hi Bryan,

Thanks for a review.

On 09/12/2014 03:11 AM, Bryan Wu wrote:
> On Wed, Aug 20, 2014 at 6:41 AM, Jacek Anaszewski
> <j.anaszewski@...sung.com> wrote:
>> Add a mechanism for locking LED subsystem sysfs interface.
>> This patch prepares ground for addition of LED Flash Class
>> extension, whose API will be integrated with V4L2 Flash API.
>> Such a fusion enforces introducing a locking scheme, which
>> will secure consistent access to the LED Flash Class device.
>>
>> The mechanism being introduced allows for disabling LED
>> subsystem sysfs interface by calling led_sysfs_lock function
>> and enabling it by calling led_sysfs_unlock. The functions
>> alter the LED_SYSFS_LOCK flag state and must be called
>> under mutex lock. The state of the lock is checked with use
>> of led_sysfs_is_locked function. Such a design allows for
>> providing immediate feedback to the user space on whether
>> the LED Flash Class device is available or is under V4L2 Flash
>> sub-device control.
>>
>> Signed-off-by: Jacek Anaszewski <j.anaszewski@...sung.com>
>> Acked-by: Kyungmin Park <kyungmin.park@...sung.com>
>> Cc: Bryan Wu <cooloney@...il.com>
>> Cc: Richard Purdie <rpurdie@...ys.net>
>> ---
>>   drivers/leds/led-class.c    |   23 ++++++++++++++++++++---
>>   drivers/leds/led-core.c     |   18 ++++++++++++++++++
>>   drivers/leds/led-triggers.c |   15 ++++++++++++---
>>   include/linux/leds.h        |   32 ++++++++++++++++++++++++++++++++
>>   4 files changed, 82 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
>> index 6f82a76..0bc0ba9 100644
>> --- a/drivers/leds/led-class.c
>> +++ b/drivers/leds/led-class.c
>> @@ -39,17 +39,31 @@ static ssize_t brightness_store(struct device *dev,
>>   {
>>          struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>          unsigned long state;
>> -       ssize_t ret = -EINVAL;
>> +       ssize_t ret;
>> +
>> +#ifdef CONFIG_V4L2_FLASH_LED_CLASS
>
> Can we remove this #ifdef? Following code looks good to the common LED class.

Sure.

>> +       mutex_lock(&led_cdev->led_lock);
>
> Can we choose more meaningful name instead of led_lock here?
> Then use led_sysfs_enable() instead of led_sysfs_unlock()
> led_sysfs_disable instead of led_sysfs_lock()
> led_sysfs_is_disabled instead of led_sysfs_is_locked()
>
> And the flag LED_SYSFS_LOCK -> LED_SYSFS_DISABLE
>
> I was just confused by the name lock and unlock and mutex lock.
>
> The idea looks good to me.

Indeed, this naming will be more intuitive.

Regards,
Jacek

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