linux-kernel - Re: [PATCH] clk: rockchip: Set "ignore unused" for PMU M0 clocks on rk3399

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Message-ID: <6585236.hCVu3AsgCt@phil>
Date:   Tue, 21 Feb 2017 18:47:13 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     linux-rockchip@...ts.infradead.org, jwerner@...omium.org,
        hl@...k-chips.com, dbasehore@...omium.org,
        zhengxing@...k-chips.com, mturquette@...libre.com,
        sboyd@...eaurora.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: rockchip: Set "ignore unused" for PMU M0 clocks on rk3399

Am Dienstag, 14. Februar 2017, 13:01:14 CET schrieb Douglas Anderson:
> The PMU Cortex M0 on rk3399 is intended to be used for things like
> DDRFreq transitions, suspend/resume, and other things that are the
> purview of ARM Trusted Firmware and not the kernel.  As such, the
> kernel shouldn't be messing with the clocks.  Add CLK_IGNORE_UNUSED to
> these clocks.
> 
> Without this change, the following was observed on a Chromebook with a
> rk3399 (using not-yet-upstream ARM Trusted Firmware code and
> not-yet-upstream kernel code based on kernel-4.4):
> 
> 1. We init the clock framework.
> 
> 2. We start up "DDRFreq", which causes ATF to occasionally fire up the
>    M0 for transitions.  Each time ATF fires up the M0 it will turn on
>    these clocks and each time it is done it will turn them off.
> 
> 3. We finally get to the the part of the kernel that calls
>    clk_disable_unused() and we disables the clocks.
> 
> You can see the race above.  Basically everything is fine as long as
> ARM Trusted Firmware isn't starting up the M0 at exactly the same time
> that the kernel is disabling unused clocks.  ...but if the race
> happens then we go boom.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

applied for 4.12

Thanks
Heiko