linux-kernel - Re: [PATCH 0/3] clk: qcom: smd-rpm: Report enable state to framework

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Message-ID: <YYpMzau3CWRQYlkJ@gerhold.net>
Date:   Tue, 9 Nov 2021 11:26:21 +0100
From:   Stephan Gerhold <stephan@...hold.net>
To:     Shawn Guo <shawn.guo@...aro.org>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] clk: qcom: smd-rpm: Report enable state to framework

Hi Shawn,

On Tue, Nov 09, 2021 at 10:25:55AM +0800, Shawn Guo wrote:
> Currently the enable state of smd-rpm clocks are not properly reported
> back to framework due to missing .is_enabled and .is_prepared hooks.
> This causes a couple of issues.
> 
> - All those unused clocks are not voted for off, because framework has
>   no knowledge that they are unused.  It becomes a problem for vlow
>   power mode support, as we do not have every single RPM clock claimed
>   and voted for off by client devices, and rely on clock framework to
>   disable those unused RPM clocks.
> 

I posted a similar patch a bit more than a year ago [1]. Back then one
of the concerns was that we might disable critical clocks just because
they have no driver using it actively. For example, not all of the
platforms using clk-smd-rpm already have an interconnect driver.
Disabling the interconnect related clocks will almost certainly make the
device lock up completely. (I tried it back then, it definitely does...)

I proposed adding CLK_IGNORE_UNUSED for the interconnect related clocks
back then [2] which would allow disabling most of the clocks at least.
Stephen Boyd had an alternative proposal to instead move the
interconnect related clocks completely out of clk-smd-rpm [3].
But I'm still unsure how this would work in a backwards compatible way. [4]

Since your patches are more or less identical I'm afraid the same
concerns still need to be solved somehow. :)

Thanks,
Stephan

[1]: https://lore.kernel.org/linux-arm-msm/20200817140908.185976-1-stephan@gerhold.net/
[2]: https://lore.kernel.org/linux-arm-msm/20200818080738.GA46574@gerhold.net/
[3]: https://lore.kernel.org/linux-arm-msm/159796605593.334488.8355244657387381953@swboyd.mtv.corp.google.com/
[4]: https://lore.kernel.org/linux-arm-msm/20200821064857.GA905@gerhold.net/