linux-kernel - Re: [PATCH v2 5/5] clk: Get runtime PM before walking tree for clk

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Date: Mon, 25 Mar 2024 12:39:49 -0700
From: Doug Anderson <dianders@...omium.org>
To: Stephen Boyd <sboyd@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>, linux-kernel@...r.kernel.org, 
	linux-clk@...r.kernel.org, patches@...ts.linux.dev, 
	linux-arm-msm@...r.kernel.org, Taniya Das <quic_tdas@...cinc.com>
Subject: Re: [PATCH v2 5/5] clk: Get runtime PM before walking tree for clk_summary

Hi,

On Mon, Mar 25, 2024 at 11:42 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Similar to the previous commit, we should make sure that all devices are
> runtime resumed before printing the clk_summary through debugfs. Failure
> to do so would result in a deadlock if the thread is resuming a device
> to print clk state and that device is also runtime resuming in another
> thread, e.g the screen is turning on and the display driver is starting
> up. We remove the calls to clk_pm_runtime_{get,put}() in this path
> because they're superfluous now that we know the devices are runtime
> resumed. This also squashes a bug where the return value of
> clk_pm_runtime_get() wasn't checked, leading to an RPM count underflow
> on error paths.

Ah, interesting. Thinking about this, I guess it means that a single
device that returns an error from its pm_runtime_get() will fully
disable the entire system's unused clock disabling as well as the
entire clk_summary. Crossing my fingers that doesn't show up in
practice...


> Fixes: 1bb294a7981c ("clk: Enable/Disable runtime PM for clk_summary")
> Cc: Taniya Das <quic_tdas@...cinc.com>
> Cc: Douglas Anderson <dianders@...omium.org>
> Signed-off-by: Stephen Boyd <sboyd@...nel.org>
> ---
>  drivers/clk/clk.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)

Reviewed-by: Douglas Anderson <dianders@...omium.org>