Re: [PATCH] bcm2835: Add Raspberry Pi CPU frequency control to the device tree

From: Eric Anholt <eric@anholt.net>
To: linux-rpi-kernel@lists.infradead.org
Cc: Lubomir Rintel <lkundrak@v3.sk>,
	Stephen Warren <swarren@wwwdotorg.org>,
	Lee Jones <lee@kernel.org>,
	linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH] bcm2835: Add Raspberry Pi CPU frequency control to the device tree
Date: Wed, 14 Oct 2015 17:29:28 -0700	[thread overview]
Message-ID: <87bnc1gejb.fsf@eliezer.anholt.net> (raw)
In-Reply-To: <1444592795-15129-1-git-send-email-lkundrak@v3.sk>

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Lubomir Rintel <lkundrak@v3.sk> writes:

> This adds a device tree binding for Broadcom BCM2834 CPU frequency control
> driven via Raspberry Pi VideoCore 4 firmware interface.
>
> Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
> Cc: Stephen Warren <swarren@wwwdotorg.org>
> Cc: Lee Jones <lee@kernel.org>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: linux-rpi-kernel@lists.infradead.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-pm@vger.kernel.org
> ---
> Depends on the RPi Firmware driver submitted on linux-rpi-kernel a while ago. 
> Can't see it in arm-soc or linux-next yet though (?). Available in branch 
> 'rpi-firmware' of https://github.com/anholt/linux

Looks like the firmware driver slipped through the cracks for 4.3.  I'll
be sending a pull request for it for 4.4.

With the cprman clock driver, we could set CPU frequency natively from
Linux.  What we get from doing things through the VPU right now are that
the MAX (overclock) setting can be set by the user in config.txt, and
the VPU does some watching of thermals to decide when to throttle back
to non-overclock.

Unless we do native thermal control from Linux (which we don't have a
driver for) to get equivalent protection, then I think we should
probably go ahead with the VPU-based cpufreq control.

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