Re: [PATCH v5 1/2] leds: core: Introduce LED pattern trigger

From: Jacek Anaszewski
Date: Fri Aug 24 2018 - 15:49:59 EST

Hi Pavel,

On 08/24/2018 12:11 PM, Pavel Machek wrote:
> Hi!
>> I think that it would be more flexible if software pattern fallback
>> was applied in case of pattern_set failure. Otherwise, it would
>> lead to the situation where LED class devices that support hardware
>> blinking couldn't be applied the same set of patterns as LED class
>> devices that don't implement pattern_set. The latter will always have to
>> resort to using software pattern engine which will accept far greater
>> amount of pattern combinations.
>> In this case we need to discuss on what basis the decision will be
>> made on whether hardware or software engine will be used.
>> Possible options coming to mind:
>> - an interface will be provided to determine max difference between
>> the settings supported by the hardware and the settings requested by
>> the user, that will result in aligning user's setting to the hardware
>> capabilities
>> - the above alignment rate will be predefined instead
>> - hardware engine will be used only if user requests supported settings
>> on the whole span of the requested pattern
>> - in each of the above cases it would be worth to think of the
>> interface to show the scope of the settings supported by hardware
> I'd recommend keeping it simple. We use hardware engine if driver
> author thinks pattern is "close enough".

The thing is that in the ledtrig-pattern v5 implementation there
is no option of using software fallback if pattern_set op
is initialized:

+ if (led_cdev->pattern_set) {
+ return led_cdev->pattern_set(led_cdev, data->patterns,
+ data->npatterns, data->repeat);
+ }

> If human can not tell the difference, it probably is.
> We may want to do something more formal later.

Best regards,
Jacek Anaszewski