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

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

On 03/22/2016 12:47 PM, Heiner Kallweit wrote:
> Am 22.03.2016 um 09:05 schrieb Jacek Anaszewski:
>> On 03/21/2016 06:34 PM, Heiner Kallweit wrote:
>>> Am 21.03.2016 um 16:35 schrieb Jacek Anaszewski:
>>>> 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@gmail.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.
>>>>
>>> No, it's not sufficient. Let's say the RGB extension is disabled and we have a RGB trigger.
>>> The check is a no-op now (returns always true), therefore the RGB trigger would be displayed
>>> in the list of available triggers also for all non-RGB LED's.
>>
>> If RGB trigger was made dependent on LED RGB class, then the related
>> Kconfig symbol would remain undefined in !CONFIG_LEDS_CLASS_RGB case.
>>
> Making a RGB trigger dependent on LED RGB class would mean to enclose all calls to trigger
> functions in the RGB trigger like this:
> #if IS_ENABLED(CONFIG_LEDS_CLASS_RGB)
> 	trigger_function()
> #endif

You probably think about the case when we have two triggers in
single module, like in the planned {rgb-}heartbeat case?

If so this is an argument for having RGB triggers in separate files.

> This would apply to led_trigger_(un)register, led_trigger_event, led_trigger_blink, etc.
> And I think it wouldn't be too nice to force other kernel modules wanting to implement
> a RGB trigger to add these conditional compile statements.

What other modules do you have on mind? LED triggers are implemented in
their own files.

> Alternatively, as mentioned before, we would have to add this to all public trigger functions:
>
> #if !IS_ENABLED(CONFIG_LEDS_CLASS_RGB)
> 	if (trig->flags & LED_TRIG_CAP_RGB))
> 		return;
> #endif
> I think this would add significant overhead w/o gaining really something.
 >
>>> We could maximum remove the "|| led_cdev->flags & LED_DEV_CAP_RGB" from the check if
>>> the RGB extension is disabled. But it's open whether this minimal gain in a non-critical
>>> code path justifies this.
>>>
>>>>>>>>>       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