linux-kernel - Re: [PATCH 2/2] clk: bcm2835: Skip PLLC clocks when deciding on a new clock parent

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Date:	Mon, 02 May 2016 08:29:30 -0700
From:	Eric Anholt <eric@...olt.net>
To:	Martin Sperl <kernel@...tin.sperl.org>
Cc:	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>
Subject: Re: [PATCH 2/2] clk: bcm2835: Skip PLLC clocks when deciding on a new clock parent

Martin Sperl <kernel@...tin.sperl.org> writes:

>> On 26.04.2016, at 21:39, Eric Anholt <eric@...olt.net> wrote:
>> 
>> If the firmware had set up a clock to source from PLLC, go along with
>> it.  But if we're looking for a new parent, we don't want to switch it
>> to PLLC because the firmware will force PLLC (and thus the AXI bus
>> clock) to different frequencies during over-temp/under-voltage,
>> without notification to Linux.
>> 
>> On my system, this moves the Linux-enabled HDMI state machine and DSI1
>> escape clock over to plld_per from pllc_per.  EMMC still ends up on
>> pllc_per, because the firmware had set it up to use that.
>> 
>> Signed-off-by: Eric Anholt <eric@...olt.net>
>> Fixes: 41691b8862e2 ("clk: bcm2835: Add support for programming the audio domain clocks")
>> —
>
> I guess this patch looks to me as if it is a policy inside the kernel,
> which is AFAIK frowned upon.

Can you come up with a use for putting peripherals on PLLC ever, such
that we need choice?

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