linux-kernel - Re: [PATCH v12 1/2] leds: core: Introduce LED pattern trigger

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180922194451.GA27826@amd>
Date:   Sat, 22 Sep 2018 21:44:51 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Baolin Wang <baolin.wang@...aro.org>, rteysseyre@...il.com,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 1/2] leds: core: Introduce LED pattern trigger

On Sat 2018-09-22 00:18:13, Pavel Machek wrote:
> On Sat 2018-09-22 00:11:29, Jacek Anaszewski wrote:
> > On 09/21/2018 11:17 PM, Pavel Machek wrote:
> > > On Fri 2018-09-21 22:59:40, Jacek Anaszewski wrote:
> > >> Hi Baolin,
> > >>
> > >> On 09/21/2018 05:31 AM, Baolin Wang wrote:
> > >>> Hi Jacek and Pavel,
> > >>>
> > >>> On 11 September 2018 at 10:47, Baolin Wang <baolin.wang@...aro.org> wrote:
> > >>>> This patch adds one new led trigger that LED device can configure
> > >>>> the software or hardware pattern and trigger it.
> > >>>>
> > >>>> Consumers can write 'pattern' file to enable the software pattern
> > >>>> which alters the brightness for the specified duration with one
> > >>>> software timer.
> > >>>>
> > >>>> Moreover consumers can write 'hw_pattern' file to enable the hardware
> > >>>> pattern for some LED controllers which can autonomously control
> > >>>> brightness over time, according to some preprogrammed hardware
> > >>>> patterns.
> > >>>>
> > >>>> Signed-off-by: Raphael Teysseyre <rteysseyre@...il.com>
> > >>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> > > 
> > >>> Do you have any comments for the v12 patch set? Thanks.
> > >>
> > >> We will probably have to remove hw_pattern from ledtrig-pattern
> > >> since we are unable to come up with generic interface for it.
> > >> Unless thread [0] will end up with some brilliant ideas. So far
> > >> we're waiting for Pavel's reply.
> > >>
> > >> [0] https://lkml.org/lkml/2018/9/13/1216
> > > 
> > > To paint a picture:
> > > 
> > > brightness
> > > 
> > >    rise hold          lower       hold down
> > >   ^    XXXXXXXXXXXXXXX
> > >   |   X               XX
> > >   |  X                  XX
> > >   | X                     XXXXXXXXXXXXXXXXXXXXXXXXXX
> > >   +-------------------------------------------------------> time
> > > 
> > > This is what Baolin's hardware can do, right?
> > > 
> > > This is also what pattern trigger can do, right?
> > > 
> > > So all we need to do is match the two interfaces, so that hw_pattern
> > > returns -EINVAL on patterns hardware can not actually do.
> > > 
> > > I believe I described code to do that in [0] above.
> > 
> > You said that we should get the same effect by writing the
> > same series of tuples to either pattern or hw_pattern file.
> > 
> > Below command consists of four tuples (marked with brackets
> > to highlight), and it will activate breathing mode in Baolin's
> > hw_pattern:
> > 
> > "[0 rise_duration] [brightness high_duration] [brightness fall_duration]
> > [0   low_duration]"
> > 
> > Now, I can't see how these four tuples could force the software
> > fallback to produce breathing effect you depicted.
> 
> I really should get some sleep now. But my intention was that software
> fallback produces just that with those four tuples. (If it does not,
> we can fix the software fallback to do just that).

And you are right, v12 1/2 seems to do the wrong thing.

My "brilliant idea" is to something closer to the original version I
posted here. I'm attaching it for reference.

I'm also attaching the original documentation. It was clearly designed
to do smooth transitions, too. (But pattern is written in slightly
different way there, AFAICT).

Clearly, having same semantics for pattern and hw_pattern is possible.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

View attachment "ledtrig-pattern.c" of type "text/x-csrc" (9591 bytes)

View attachment "ledtrig-pattern.txt" of type "text/plain" (2739 bytes)

Download attachment "signature.asc" of type "application/pgp-signature" (182 bytes)