linux-kernel - Re: PM regression with LED changes in next-20161109

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Date:   Tue, 15 Nov 2016 11:09:24 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Jacek Anaszewski <j.anaszewski@...sung.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     Tony Lindgren <tony@...mide.com>, linux-leds@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Darren Hart <dvhart@...radead.org>
Subject: Re: PM regression with LED changes in next-20161109

Hi,

On 15-11-16 11:01, Jacek Anaszewski wrote:
> Hi,
>
> On 11/14/2016 01:51 PM, Hans de Goede wrote:

<snip>

>> Ugh, I see I accidentally send a v4 twice, instead of
>> calling the version which dropped those called v5 as
>> I should have, sorry.
>>
>> The v4 which I would like to see merged, the one with
>> those calls dropped, is here:
>>
>> https://patchwork.kernel.org/patch/9423093/
>
> Right I've had an impression that I've already seen something
> different than "first" v4.
>
> Regarding the patch - adding led_notify_brightness_change() to
> brightness_store() can have similar power consumption related
> implications if brightness is set frequently via sysfs.

That means that userspace is waking up frequently to write the
sysfs file, so in that case userspace is already draining
a lot of energy, so I don't think that is something we need to
worry about.

> I'm leaning
> towards adding a new brightness file similar to user_brightness
> discussed in this thread.
>
> It would cover shortcomings and read/write inconsistencies that
> brightness file currently has, but without breaking existing users.
>
> I'd not however go for "user_brightness" name due to the possible
> brightness adjustments made autonomously by firmware. I'm afraid
> that devising a meaningful name for the new file will be hard,
> so the simplest would be just brighntess2. Dedicated section
> in leds-class.txt should be devoted to it.

Ok, let me quote myself from another part of this thread:

We've 2 sorts of brightness really:

1) transient brightness, aka current brightness, when blinking or
triggers are used this will switch many times a second
between off and some on level.

2) non-transient brightness, for non blinking leds this is the
actual brightness, for blinking leds this is the brightness
level used when the led is on.

Now we want to have a sysfs attribute reflecting 2, so that
userspace can poll on that, both for my use-case as well as so
that userspace process a can detect changes made by writing to
the brightness file by process b.

So maybe we need to simply call the new attribute
non_transient_brightness instead of user_brightness?

non_transient_brightness certainly seems like a better name
then brightness2 ?

Regards,

Hans