From: j.anaszewski@samsung•com (Jacek Anaszewski)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v6 5/5] leds: netxbig: set led_classdev max_brightness
Date: Mon, 28 Sep 2015 12:15:22 +0200 [thread overview]
Message-ID: <5609133A.3050802@samsung.com> (raw)
In-Reply-To: <20150928091956.GY7306@kw.sim.vm.gnt>
On 09/28/2015 11:19 AM, Simon Guinot wrote:
> On Mon, Sep 28, 2015 at 10:02:35AM +0200, Jacek Anaszewski wrote:
>> Hi Simon,
>
> Hi Jacek,
>
>>
>> Does your device support reading the brightness currently set?
>
> No it don't.
>
>> If so, it would be good to implement brightness_get op, because
>> AFAIR you mentioned that the firmware you are working with sets
>> always maximum brightness value. Having the op implemented would
>> allow to find this out.
>
> I don't understand how this can help. I mean, the only issue is that at
> startup the initial LED state is unknown. And the software brightness
> value could be false. But once the LED is configured, the brightness
> values for software and hardware are synchronized. The brightness value
> is stored/cached in led_classdev and it can be retrieved by the user via
> sysfs...
>
> For my own knowledge, is there some interest in having brightness_get(),
> aside of guessing the LED initial state ?
Some LED controllers can adjust brightness in case battery voltage level
falls below some threshold.
> What does the embedded firmware is writing 255 or 0 into the brightness
> sysfs attribute. The max_brightness value is ignored. After this patch,
> writing 255 and 0 still allows to configure the LED in the same way:
> maximum brightness or off. Thus, I believe there is no compatibility
> issue.
LED core always assures that brightness value passed to brightness_set
op does not exceed max_brightness value. So, now after executing
"echo 255 > brightness", LED core will adjust it to max_brightness
(e.g. 7) before passing to brightness_set.
In the message [1], you mentioned that "LEDs are only enabled at their
maximum level", so IIUC following is possible:
#echo 3 > "brightness"
firmware sets brightness to max_brightness from DT (e.g. 7), but
#cat brightness
#3
Is it true?
> But of course, I will update the firmware as well :)
[1] http://www.spinics.net/lists/devicetree/msg94358.html
--
Best Regards,
Jacek Anaszewski
next prev parent reply other threads:[~2015-09-28 10:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-26 21:02 [PATCH v6 0/5] Add DT support for netxbig LEDs Simon Guinot
2015-09-26 21:02 ` [PATCH v6 1/5] leds: netxbig: add device tree binding Simon Guinot
2015-09-26 21:02 ` [PATCH v6 2/5] ARM: Kirkwood: add LED DT entries for netxbig boards Simon Guinot
2015-09-26 21:02 ` [PATCH v6 3/5] ARM: mvebu: remove static LED setup " Simon Guinot
2015-09-26 21:02 ` [PATCH v6 4/5] leds: netxbig: convert to use the devm_ functions Simon Guinot
2015-09-26 21:02 ` [PATCH v6 5/5] leds: netxbig: set led_classdev max_brightness Simon Guinot
2015-09-28 8:02 ` Jacek Anaszewski
2015-09-28 9:19 ` Simon Guinot
2015-09-28 10:15 ` Jacek Anaszewski [this message]
2015-09-28 11:50 ` Simon Guinot
2015-09-28 12:24 ` Jacek Anaszewski
2015-09-28 13:25 ` Simon Guinot
2015-09-28 13:43 ` Jacek Anaszewski
2015-10-09 9:43 ` [PATCH v6 0/5] Add DT support for netxbig LEDs Jacek Anaszewski
2015-10-15 7:16 ` Gregory CLEMENT
2015-10-15 8:11 ` Jacek Anaszewski
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