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

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Date:   Wed, 2 Jan 2019 11:55:22 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Russell King <linux@...linux.org.uk>,
        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>
Subject: Re: [PATCH v3 1/4] clk: core: clarify the check for runtime PM

Hi Stephen,

Stephen Boyd <sboyd@...nel.org> wrote on Thu, 20 Dec 2018 13:09:19
-0800:

> Quoting Miquel Raynal (2018-12-19 00:03:31)
> > Hi Stephen,
> > 
> > Stephen Boyd <sboyd@...nel.org> wrote on Tue, 18 Dec 2018 16:03:29
> > -0800:
> >   
> > > 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.  
> > 
> > Sure, I'll do that if you think there is a danger.  
> 
> I've made the change and pushed it out to the clk tree. I'm working on
> some patches to change how we do parent lookups and reworking clk_get()
> in the process. Take a look so we don't duplicate efforts. The code
> isn't complete, but I hope to finish soon. Your device links patches can
> build upon this.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git clk-parent-rewrite
> 

Sorry for the delay and thanks for the update. I have been preempted by
another issue, I will switch to clocks and propose something ASAP.


Thanks,
Miquèl