From: Jacek Anaszewski <jacek.anaszewski@gmail.com>
To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Linux LED Subsystem <linux-leds@vger.kernel.org>,
linux-gpio@vger.kernel.org,
Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Pavel Machek <pavel@ucw.cz>, Dan Murphy <dmurphy@ti.com>
Subject: Re: [PATCH] leds: gpio: support multi-level brightness
Date: Wed, 9 Oct 2019 20:14:21 +0200 [thread overview]
Message-ID: <aa269811-c66c-da6a-ce2a-7a25fe22d2e5@gmail.com> (raw)
In-Reply-To: <CAC5umyjRbVFV8hQoynA83wEAwumMU1iZ1KouHaXiNruwXfATZQ@mail.gmail.com>
On 10/9/19 4:43 PM, Akinobu Mita wrote:
> 2019年10月9日(水) 5:53 Jacek Anaszewski <jacek.anaszewski@gmail.com>:
>>
>> On 10/6/19 4:11 PM, Akinobu Mita wrote:
>>> 2019年10月6日(日) 4:17 Jacek Anaszewski <jacek.anaszewski@gmail.com>:
>>>>
>>>> On 10/5/19 3:20 PM, Akinobu Mita wrote:
>>>>> 2019年10月5日(土) 6:17 Jacek Anaszewski <jacek.anaszewski@gmail.com>:
>>>>>>
>>>>>> Hi Akinobu,
>>>>>>
>>>>>> Why do you think this change is needed? Does it solve
>>>>>> some use case for you?
>>>>>
>>>>> It can be useful when using with an LED trigger that could set the
>>>>> brightness values other than LED_FULL or LED_OFF.
>>>>>
>>>>> The LED CPU trigger for all CPUs (not per CPU) sets the brightness value
>>>>> depending on the number of active CPUs. We can define the multi brightness
>>>>> level gpio LED with fewer number of GPIO LEDs than the total number of
>>>>> CPUs, and the LEDs can be viewed as a level meter.
>>>>
>>>> Can't you achieve exactly the same effect by creating separate LED class
>>>> device for each GPIO LED and registering each of them for separate cpuN
>>>> trigger?
>>>
>>> If there are GPIO LEDs as many as the total number of CPUs, we can.
>>> However, if there are only two GPIO LEDs and six CPUs, we can only know
>>> the CPU activity for two CPUs out of six CPUs with cpuN trigger.
>>> So it's different from using cpu (all) trigger with multi level (2-level)
>>> brightness GPIO LED.
>>
>> OK, that's a reasonable argument. However, this is clearly
>> trigger-specific functionality and we should not delegate this
>> logic down to the driver.
>>
>> What you propose should be a responsibility of a trigger that would
>> allow registering multiple LEDs for its disposal. This would have to
>> be different from existing LED Trigger mechanism, that blindly
>> applies trigger event to all LEDs that have registered for it.
>>
>> Such a trigger would have to be a separate LED (pattern?) class device.
>> It would need to be told how many LEDs it is going to manage
>> and create files for filling the LED names. This design could be also
>> used for defining patterns spanning on multiple LEDs. Just a rough idea.
>> We can dwell on it if it catches.
>
> What do you think about introducing a new led driver and describing a
> level meter in the following DT node.
>
> led-level-meter {
> compatible = "led-level-meter";
> leds = <&led0>, <&led1>, <&led2>, <&led3>;
> };
>
> Setting the brightness of led-level-meter to LED_HALF turns on led0 and
> led1 with max brightness and turns off led2 and led3.
>
> This is inspired by led-backlight driver patchset and Bjorn Andersson's
> reply in this thread.
Looks interesting, I like the idea.
--
Best regards,
Jacek Anaszewski
next prev parent reply other threads:[~2019-10-09 18:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 15:34 [PATCH] leds: gpio: support multi-level brightness Akinobu Mita
2019-10-04 15:42 ` Dan Murphy
2019-10-05 13:13 ` Akinobu Mita
2019-11-04 9:09 ` Pavel Machek
2019-10-04 21:17 ` Jacek Anaszewski
2019-10-05 13:20 ` Akinobu Mita
2019-10-05 19:17 ` Jacek Anaszewski
2019-10-06 14:11 ` Akinobu Mita
2019-10-08 20:53 ` Jacek Anaszewski
2019-10-09 14:43 ` Akinobu Mita
2019-10-09 18:14 ` Jacek Anaszewski [this message]
2019-10-06 4:06 ` Bjorn Andersson
2019-10-06 14:13 ` Akinobu Mita
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