linux-kernel - Re: [PATCH 1/2] clk: ti: add a usecount for autoidle

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Message-ID: <20181110085243.7da163b9@kemnade.info>
Date:   Sat, 10 Nov 2018 08:52:43 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Tero Kristo <t-kristo@...com>
Cc:     <mturquette@...libre.com>, <sboyd@...nel.org>,
        <linux-omap@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bcousson@...libre.com>,
        <paul@...an.com>, <tony@...mide.com>,
        <letux-kernel@...nphoenux.org>
Subject: Re: [PATCH 1/2] clk: ti: add a usecount for autoidle

On Thu, 8 Nov 2018 12:36:35 +0200
Tero Kristo <t-kristo@...com> wrote:

> On 04/10/2018 23:38, Andreas Kemnade wrote:
> > We have the scenario that first autoidle is disabled for all clocks,
> > then it is disabled for selected ones and then enabled for all. So
> > we should have some counting here, also according to the
> > comment in  _setup_iclk_autoidle()
> > 
> > Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > ---
> >   drivers/clk/ti/autoidle.c | 32 ++++++++++++++++++++++++--------
> >   include/linux/clk/ti.h    |  1 +
> >   2 files changed, 25 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/clk/ti/autoidle.c b/drivers/clk/ti/autoidle.c
> > index 7bb9afbe4058..bb6cff168e73 100644
> > --- a/drivers/clk/ti/autoidle.c
> > +++ b/drivers/clk/ti/autoidle.c
> > @@ -37,6 +37,14 @@ struct clk_ti_autoidle {
> >   static LIST_HEAD(autoidle_clks);
> >   static LIST_HEAD(clk_hw_omap_clocks);
> >   
> > +/*
> > + * we have some non-atomic read/write
> > + * operations behind it, so lets
> > + * take one mutex for handling autoidle
> > + * of all clocks
> > + */
> > +static DEFINE_MUTEX(autoidle_mutex);  
> 
> Why mutex? This prevents calling the autoidle APIs from atomic context. 
> Did you check the mutex debug kernel configs with this?
> 
Oops, I thought they were on, but they were not. OK,
I am preparing a v2 of this thing.


> This may cause problems with the runtime PM entries to the code at least.
> 
> 
> > +
> >   /**
> >    * omap2_clk_deny_idle - disable autoidle on an OMAP clock
> >    * @clk: struct clk * to disable autoidle for
> > @@ -48,8 +56,13 @@ int omap2_clk_deny_idle(struct clk *clk)
> >   	struct clk_hw_omap *c;
> >   
> >   	c = to_clk_hw_omap(__clk_get_hw(clk));
> > -	if (c->ops && c->ops->deny_idle)
> > -		c->ops->deny_idle(c);
> > +	if (c->ops && c->ops->deny_idle) {
> > +		mutex_lock(&autoidle_mutex);
> > +		c->autoidle_count--;
> > +		if (c->autoidle_count == -1)  
> 
> I think you should swap the arithmetics here, all the other usecounters 
> use positive values, here you enter deep to the negative side when 
> autoidle is denied by multiple users, which might be confusing.
> 
agreed.

Regards,
Andreas

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