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

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Message-ID: <CABxcv=m8X1o=5vo1CdpozD2YgfVZUq663+etc-ywGwBPvSs1Qw@mail.gmail.com>
Date:   Wed, 15 Feb 2017 14:06:03 -0300
From:   Javier Martinez Canillas <javier@...hile0.org>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     Douglas Anderson <dianders@...omium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        jwerner@...omium.org, hl@...k-chips.com, dbasehore@...omium.org,
        zhengxing@...k-chips.com,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>, linux-clk@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: rockchip: Set "ignore unused" for PMU M0 clocks on rk3399

Hello Heiko and Doug,

On Wed, Feb 15, 2017 at 2:01 PM, Heiko Stübner <heiko@...ech.de> wrote:
> Am Mittwoch, 15. Februar 2017, 12:27:59 CET schrieb Javier Martinez Canillas:
>> Hello Doug,
>>
>> On Tue, Feb 14, 2017 at 6:01 PM, Douglas Anderson <dianders@...omium.org>
> wrote:
>> > 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.
>>
>> Isn't CLK_IS_CRITICAL a more suitable flag for this case?
>
> From the patch description it looks like the clock is expected to be
> controlled from firmware in most cases as I guess the Cortex M0 will be used
> for that all the time now. And the clock is not expected to run all the time.
>
> So I'd think clk_ignore_unused is the correct one. The whole clock-subtree for
> these clocks also does not get affected by other clocks, as it is
> independendly coming from PLLs.
>
>

I see. Thanks a lot for your explanations. I just asked because
CLK_IGNORE_UNUSED only prevents the clock to be disabled by
clk_disable_unused() but still can be disabled if a driver explicitly
looks it up and calls clk_disable() or if the clock is affected by
other clocks.

But I understand now that both scenarios are not possible. So yes,
CLK_IGNORE_UNUSED is more suitable in this case.

> Heiko

Best regards,
Javier