linux-kernel - Re: [PATCH 1/3] leds: triggers: add support for RGB triggers

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Date:	Mon, 21 Mar 2016 16:35:56 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Heiner Kallweit <hkallweit1@...il.com>
Cc:	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] leds: triggers: add support for RGB triggers

On 03/19/2016 08:11 PM, Heiner Kallweit wrote:
> Am 18.03.2016 um 14:10 schrieb Jacek Anaszewski:
>> On 03/17/2016 08:53 PM, Heiner Kallweit wrote:
>>> Am 17.03.2016 um 14:41 schrieb Jacek Anaszewski:
>>>> Hi Heiner,
>>>>
>>>> On 03/13/2016 06:14 PM, Heiner Kallweit wrote:
>>>>> Add basic support for RGB triggers. Triggers with flag LED_TRIG_CAP_RGB
>>>>> set are available to RGB LED devices only.
>>>>>
>>>>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>>>>> ---
>>>>>     drivers/leds/led-triggers.c | 15 ++++++++++++---
>>>>>     include/linux/leds.h        |  3 +++
>>>>>     2 files changed, 15 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
>>>>> index 2181581..3ccf88b 100644
>>>>> --- a/drivers/leds/led-triggers.c
>>>>> +++ b/drivers/leds/led-triggers.c
>>>>> @@ -30,6 +30,13 @@ static LIST_HEAD(trigger_list);
>>>>>
>>>>>      /* Used by LED Class */
>>>>>
>>>>> +static inline bool led_trig_check_rgb(struct led_trigger *trig,
>>>>> +                      struct led_classdev *led_cdev)
>>>>> +{
>>>>> +    return !(trig->flags & LED_TRIG_CAP_RGB) ||
>>>>> +           led_cdev->flags & LED_DEV_CAP_RGB;
>>>>> +}
>>>>
>>>> Could you explain what is the purpose of this function?
>>>> What actually do we want to check here?
>>>>
>>> Triggers using RGB functionality can't be used with non-RGB LED's.
>>> This check checks for such unsupported combinations:
>>> It returns false if the trigger uses RGB functionality but LED doesn't
>>> support the RGB extension.
>>
>> We need more meaningful name for it. Maybe led_trigger_is_supported() ?
>> And let's make it no-op for !CONFIG_LEDS_CLASS_RGB case.
>>
> OK, led_trigger_is_supported() is better.
>
> Making the function a no-op in the non-RGB case would have some impact:
> We'd have to make sure that all public trigger functions are a de-facto no-op
> for RGB triggers (at least register / unregister). Means we would need
> something like this in each public trigger function:
>
> #if !IS_ENABLED(CONFIG_LEDS_CLASS_RGB)
> 	if (trig->flags & LED_TRIG_CAP_RGB))
> 		return;
> #endif
>
> I think this would add a lot of overhead and therefore IMHO it's better to
> not make the check function a no-op.

Wouldn't it suffice to make the no-op returning true?
Preventing RGB trigger registration for non-RGB LED class configuration
seems to be different thing, also to be considered.

>>>>>     ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
>>>>>             const char *buf, size_t count)
>>>>>     {
>>>>> @@ -52,12 +59,12 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
>>>>>         down_read(&triggers_list_lock);
>>>>>         list_for_each_entry(trig, &trigger_list, next_trig) {
>>>>>             if (sysfs_streq(buf, trig->name)) {
>>>>> +            if (!led_trig_check_rgb(trig, led_cdev))
>>>>> +                break;
>>>
>>> Check for the case that userspace wants to set a RGB trigger for a non-RGB LED via sysfs.
>>>
>>>>>                 down_write(&led_cdev->trigger_lock);
>>>>>                 led_trigger_set(led_cdev, trig);
>>>>>                 up_write(&led_cdev->trigger_lock);
>>>>> -
>>>>> -            up_read(&triggers_list_lock);
>>>>> -            goto unlock;
>>>>> +            break;
>>
>> This seems to be an unrelated cleanup. Please submit it separately.
>>
> OK
>
>>>>>             }
>>>>>         }
>>>>>         up_read(&triggers_list_lock);
>>>>> @@ -84,6 +91,8 @@ ssize_t led_trigger_show(struct device *dev, struct device_attribute *attr,
>>>>>             len += sprintf(buf+len, "none ");
>>>>>
>>>>>         list_for_each_entry(trig, &trigger_list, next_trig) {
>>>>> +        if (!led_trig_check_rgb(trig, led_cdev))
>>>>> +            continue;
>>>
>>> Omit RGB triggers when listing the available triggers for a non-RGB LED via sysfs.
>>>
>>>>>             if (led_cdev->trigger && !strcmp(led_cdev->trigger->name,
>>>>>                                 trig->name))
>>>>>                 len += sprintf(buf+len, "[%s] ", trig->name);
>>>>> diff --git a/include/linux/leds.h b/include/linux/leds.h
>>>>> index 58e22e6..07eb074 100644
>>>>> --- a/include/linux/leds.h
>>>>> +++ b/include/linux/leds.h
>>>>> @@ -248,6 +248,9 @@ enum led_brightness led_hsv_to_rgb(enum led_brightness hsv);
>>>>>     struct led_trigger {
>>>>>         /* Trigger Properties */
>>>>>         const char     *name;
>>>>> +    u8        flags;
>>>>> +#define LED_TRIG_CAP_RGB    BIT(0)
>>>>> +
>>>>>         void        (*activate)(struct led_classdev *led_cdev);
>>>>>         void        (*deactivate)(struct led_classdev *led_cdev);
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>
>
>


-- 
Best regards,
Jacek Anaszewski