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

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Date:   Fri, 24 Aug 2018 21:49:50 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Baolin Wang <baolin.wang@...aro.org>, rteysseyre@...il.com,
        bjorn.andersson@...aro.org, broonie@...nel.org,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] leds: core: Introduce LED pattern trigger

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