linux-kernel - Re: [PATCH v3 1/4] clk: core: clarify the check for runtime PM

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Message-ID: <154517780935.238328.764268020422357561@swboyd.mtv.corp.google.com>
Date:   Tue, 18 Dec 2018 16:03:29 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Russell King <linux@...linux.org.uk>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Subject: Re: [PATCH v3 1/4] clk: core: clarify the check for runtime PM

Quoting Miquel Raynal (2018-12-04 11:24:37)
> Currently, the core->dev entry is populated only if runtime PM is
> enabled. Doing so prevents accessing the device structure in any
> case.
> 
> Keep the same logic but instead of using the presence of core->dev as
> the only condition, also check the status of
> pm_runtime_enabled(). Then, we can set the core->dev pointer at any
> time as long as a device structure is available.
> 
> This change will help supporting device links in the clock subsystem.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  drivers/clk/clk.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index af011974d4ec..b799347c5fd6 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -97,7 +97,7 @@ static int clk_pm_runtime_get(struct clk_core *core)
>  {
>         int ret = 0;
>  
> -       if (!core->dev)
> +       if (!core->dev || !pm_runtime_enabled(core->dev))

This looks potentially dangerous. What if runtime PM is disabled for the
clk when this function is called? Shouldn't we just stash a bool away in
the clk_core structure when it's registered? And then we can replace the
check for !core->dev with a check for 'core->rpm_enabled' instead. That
would be a more exact transformation.