linux-kernel - Re: [PATCH 08/25] media: atmel: properly get pm

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Message-ID: <20210616100314.143a5bb5@coco.lan>
Date:   Wed, 16 Jun 2021 10:03:14 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     <Eugen.Hristev@...rochip.com>
Cc:     <Jonathan.Cameron@...wei.com>, <linuxarm@...wei.com>,
        <mauro.chehab@...wei.com>, <alexandre.belloni@...tlin.com>,
        <Ludovic.Desroches@...rochip.com>, <mchehab@...nel.org>,
        <Nicolas.Ferre@...rochip.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <Claudiu.Beznea@...rochip.com>
Subject: Re: [PATCH 08/25] media: atmel: properly get pm_runtime

Em Thu, 10 Jun 2021 12:00:42 +0000
<Eugen.Hristev@...rochip.com> escreveu:

> On 6/10/21 12:38 PM, Mauro Carvalho Chehab wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > Em Thu, 10 Jun 2021 09:04:07 +0000
> > <Eugen.Hristev@...rochip.com> escreveu:
> >   
> >>>> diff --git a/drivers/media/platform/atmel/atmel-isc-base.c b/drivers/media/platform/atmel/atmel-isc-base.c
> >>>> index fe3ec8d0eaee..ce8e1351fa53 100644
> >>>> --- a/drivers/media/platform/atmel/atmel-isc-base.c
> >>>> +++ b/drivers/media/platform/atmel/atmel-isc-base.c
> >>>> @@ -294,9 +294,13 @@ static int isc_wait_clk_stable(struct clk_hw *hw)
> >>>>    static int isc_clk_prepare(struct clk_hw *hw)
> >>>>    {
> >>>>         struct isc_clk *isc_clk = to_isc_clk(hw);
> >>>> +     int ret;
> >>>>
> >>>> -     if (isc_clk->id == ISC_ISPCK)
> >>>> -             pm_runtime_get_sync(isc_clk->dev);
> >>>> +     if (isc_clk->id == ISC_ISPCK) {
> >>>> +             ret = pm_runtime_resume_and_get(isc_clk->dev);
> >>>> +             if (ret < 0)
> >>>> +                     return ret;
> >>>> +     }  
> >>
> >> Hi Mauro,
> >>
> >> With this patch, the ISC is broken on latest media tree. It looks like
> >> pm_runtime_resume_and_get for the ISC_ISPCK clock returns -ENOACCESS and
> >> thus, the probe of the driver fails:
> >>
> >> atmel-sama5d2-isc f0008000.isc: failed to enable ispck: -13
> >> atmel-sama5d2-isc: probe of f0008000.isc failed with error -13
> >>
> >>
> >> Could you point out how I could fix this ? Maybe the isc_clk->dev is not
> >> properly handled/initialized in some other part of the code ?  
> > 
> > Looking at RPM implementation:
> > 
> >          static int rpm_resume(struct device *dev, int rpmflags)
> >          {
> > ...
> >          if (dev->power.runtime_error)
> >                  retval = -EINVAL;
> >          else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> >              && dev->power.runtime_status == RPM_ACTIVE)
> >                  retval = 1;
> >          else if (dev->power.disable_depth > 0)
> >                  retval = -EACCES;
> > ...
> > 
> > It sounds that RPM is disabled for this clock. Did you call
> > pm_runtime_enable() before calling isc_clk_prepare()?
> > 
> > Thanks,
> > Mauro
> >   
> 
> I tried to call pm_runtime_enable for the clk at clk_init time, but 
> doing that makes the runtime for the ISC fail like this:
> 
> atmel-sama5d2-isc f0008000.isc: Unbalanced pm_runtime_enable!

Making RPM balanced is complex ;-)

Yet, clearly there's something weird at the PM code. I mean,
ignoring a -ENOACCESS error like the original code sounds wrong,
as it basically means that pm_runtime_get_sync() were doing
nothing (except by incrementing a refcount).

Some drivers call clk_prepare()/clk_unprepare() at their
.prepare/.unprepare ops. Those functions internally call
RPM get logic recursively, to ensure that the RPM
state of the parents are also at the right state.

Thanks,
Mauro