From: Pavel Machek <pavel@ucw.cz>
To: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: David Lechner <david@lechnology.com>,
Baolin Wang <baolin.wang@linaro.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Mark Brown <broonie@kernel.org>,
Linux LED Subsystem <linux-leds@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/2] leds: core: Introduce generic pattern interface
Date: Tue, 17 Jul 2018 23:07:00 +0200 [thread overview]
Message-ID: <20180717210700.GA9090@amd> (raw)
In-Reply-To: <8c07a016-d77d-4799-b005-6a9ea94954ce@gmail.com>
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Hi!
> >>- different hardware means via which brightness is set (MMIO, I2C, SPI,
> >> PWM and other pulsed fashion based protocols),
> >>- the need for deferring brightness setting to a workqueue task to
> >> allow for setting LED brightness from atomic context,
> >>- contention on locks
> >
> >I disagree here. Yes, it would be hard to synchronize blinking down to
> >microseconds, but it would be easy to get synchronization right down
> >to miliseconds and humans will not be able to tell the difference.
>
> There have been problems with blink interval stability close to
> 1ms, and thus there were some attempts of employing hr timers,
> which in turn introduced a new class of issues related to
> system performance etc.
Yeah, well. This is LED subsystem. Noone should program blink
intervals at 1 msec.
> >>For the LEDs driven by the same chip it would make more sense
> >>to allow for synchronization, but it can be achieved on driver
> >>level, with help of some subsystem level interface to indicate
> >>which LEDs should be synchronized.
> >>
> >>However, when we start to pretend that we can synchronize the
> >>devices, we must answer how accurate we can be. The accuracy
> >>will decrease as blink frequency rises. We'd need to define
> >>reliability limit.
> >
> >We don't need _that_ ammount of overengineering. We just need to
> >synchronize them well enough :-).
>
> Well, it would be disappointing for the users to realize that
> they don't get the effect advertised by the ABI documentation.
Linux is always best-effort, w.r.t. timing. And we can do well enough
that user will not see anything bad on "normal" systems.
> >>We've had few attempts of approaching the subject of synchronized
> >>blinking but none of them proved to be good enough to be merged.
> >
> >I'm sure interested person could do something like that in less than
> >two weeks fulltime... It is not rocket science, just a lot of work in
> >kernel...
> >
> >But patterns are few years overdue and I believe we should not delay
> >them any further.
> >
> >So... I guess I agree with Jacek in the end :-).
>
> How about taking Baolin's patches as of v5? Later, provided that
> the pattern trigger yet to be implemented will create pattern file
> on activation, we'll need to initialize default-trigger DT property,
> to keep the interface unchanged.
I have yet to look at the v5 of patches. But I agree that we do not
need to design synchronization at this moment.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2018-07-17 21:07 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-29 5:03 [PATCH v3 1/2] leds: core: Introduce generic pattern interface Baolin Wang
2018-06-29 5:03 ` [PATCH v3 2/2] leds: sc27xx: Add pattern_set/get/clear interfaces for LED controller Baolin Wang
2018-07-11 11:02 ` [PATCH v3 1/2] leds: core: Introduce generic pattern interface Baolin Wang
2018-07-11 21:10 ` Jacek Anaszewski
2018-07-12 12:24 ` Baolin Wang
2018-07-12 21:41 ` Jacek Anaszewski
2018-07-13 1:58 ` Baolin Wang
2018-07-14 21:20 ` Pavel Machek
2018-07-14 22:02 ` Jacek Anaszewski
2018-07-14 22:29 ` Pavel Machek
2018-07-14 22:39 ` Pavel Machek
2018-07-15 12:22 ` Jacek Anaszewski
2018-07-16 1:00 ` David Lechner
2018-07-16 20:29 ` Jacek Anaszewski
2018-07-16 21:56 ` Pavel Machek
2018-07-17 20:26 ` Jacek Anaszewski
2018-07-17 21:07 ` Pavel Machek [this message]
2018-07-24 0:35 ` Bjorn Andersson
2018-07-18 7:56 ` Pavel Machek
2018-07-18 11:32 ` Baolin Wang
2018-07-18 12:08 ` Pavel Machek
2018-07-18 17:00 ` David Lechner
2018-07-20 19:11 ` Jacek Anaszewski
2018-07-24 0:55 ` Bjorn Andersson
2018-07-18 18:54 ` Jacek Anaszewski
2018-07-18 19:22 ` Jacek Anaszewski
2018-07-18 22:13 ` David Lechner
2018-07-18 22:17 ` Pavel Machek
2018-07-19 20:20 ` Pavel Machek
2018-07-20 18:08 ` Jacek Anaszewski
2018-07-23 6:59 ` Baolin Wang
2018-07-24 11:41 ` Pavel Machek
2018-07-27 5:15 ` Baolin Wang
2018-07-27 8:36 ` Pavel Machek
2018-07-27 8:41 ` Baolin Wang
2018-07-24 11:50 ` Pavel Machek
2018-07-24 0:18 ` Bjorn Andersson
2018-07-16 11:08 ` Baolin Wang
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