From: bgat@billgatliff•com (Bill Gatliff)
To: linux-arm-kernel@lists•infradead.org
Subject: Montreal Linux Power Management Mini-Summit, July 13, 2009 - Meeting Notes
Date: Tue, 01 Sep 2009 21:25:20 -0500 [thread overview]
Message-ID: <4A9DD790.50302@billgatliff.com> (raw)
In-Reply-To: <63386a3d0909011522m7a175d3eyb3bbe8a29a5fd104@mail.gmail.com>
Linus Walleij wrote:
> I've felt a need for clock notifiers and we've cheated by using
> CPUfreq because it so happens that the clocking in system-wide
> and whenever the CPU freq change so may the other clocks.
>
> But if I put code into a PrimeCell MMC/SPI/I2C driver or whatever and
> use CPUfreq that's very unelegant, and for other platforms where
> the CPU freq don't change when this particular device clk freq
> change plain misleading.
>
> A clk pre/postchange notifier pair would really help and would
> make for elegant drivers that can handle clock freq transitions.
>
A lot of ARM chips have peripherals that are driven by PLLs that run
quasi-independently of the CPU clock.
If I guess correctly at what is being described above, a notifier chain
for the users of a clock would be a clean way for peripherals to deal
with clock speed *and* CPU speed changes, indeed. A clock source that
was affected by cpufreq would place itself on the cpufreq notifier
chain, and also provide a notifier chain for peripherals that are driven
by that clock. When a cpufreq notification arrived, if the clock
couldn't adjust for the cpufreq change it would use its notifier chain
to tell all downstream peripherals about it.
A lot of peripherals could then focus just on the clock notifier chain,
and would no longer care about cpufreq. I like it.
b.g.
--
Bill Gatliff
bgat at billgatliff.com
next prev parent reply other threads:[~2009-09-02 2:25 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <alpine.LFD.2.00.0905211430220.4390@localhost.localdomain>
[not found] ` <alpine.LFD.2.00.0907301801240.17818@localhost.localdomain>
2009-09-01 22:22 ` Montreal Linux Power Management Mini-Summit, July 13, 2009 - Meeting Notes Linus Walleij
2009-09-02 2:25 ` Bill Gatliff [this message]
2009-09-02 8:36 ` [linux-pm] " Francesco VIRLINZI
2009-09-02 21:44 ` Linus Walleij
2009-09-02 21:58 ` Russell King - ARM Linux
2009-09-03 14:50 ` Francesco VIRLINZI
2009-09-03 17:12 ` Russell King - ARM Linux
2009-09-03 20:15 ` Linus Walleij
2009-09-03 21:28 ` Woodruff, Richard
2009-09-04 7:34 ` Francesco VIRLINZI
2009-10-18 17:28 ` Linus Walleij
2009-10-19 7:44 ` Francesco VIRLINZI
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