linux-kernel - Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from exynos5_counters

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Date:   Mon, 17 Aug 2020 14:07:24 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-samsung-soc@...r.kernel.org,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from
 exynos5_counters_get()

On Tue, Aug 04, 2020 at 01:38:11PM +0100, Lukasz Luba wrote:
> 
> 
> On 8/4/20 1:19 PM, Marek Szyprowski wrote:
> > Hi Lukasz,
> > 
> > On 04.08.2020 11:11, Lukasz Luba wrote:
> > > Hi Marek,
> > > 
> > > On 8/4/20 7:12 AM, Marek Szyprowski wrote:
> > > > exynos5_counters_get() might fail with -EPROBE_DEFER if the driver for
> > > > devfreq event counter is not yet probed. Propagate that error value to
> > > > the caller to ensure that the exynos5422-dmc driver will be probed again
> > > > when devfreq event contuner is available.
> > > > 
> > > > This fixes boot hang if both exynos5422-dmc and exynos-ppmu drivers are
> > > > compiled as modules.
> > > > 
> > > > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > > > ---
> > > >    drivers/memory/samsung/exynos5422-dmc.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/memory/samsung/exynos5422-dmc.c
> > > > b/drivers/memory/samsung/exynos5422-dmc.c
> > > > index b9c7956e5031..639811a3eecb 100644
> > > > --- a/drivers/memory/samsung/exynos5422-dmc.c
> > > > +++ b/drivers/memory/samsung/exynos5422-dmc.c
> > > > @@ -914,7 +914,7 @@ static int exynos5_dmc_get_status(struct device
> > > > *dev,
> > > >        } else {
> > > >            ret = exynos5_counters_get(dmc, &load, &total);
> > > >            if (ret < 0)
> > > > -            return -EINVAL;
> > > > +            return ret;
> > > >              /* To protect from overflow, divide by 1024 */
> > > >            stat->busy_time = load >> 10;
> > > > 
> > > 
> > > Thank you for the patch, LGTM.
> > > Some questions are still there, though. The function
> > > exynos5_performance_counters_init() should capture that the counters
> > > couldn't be enabled or set. So the functions:
> > > exynos5_counters_enable_edev() and exynos5_counters_set_event()
> > > must pass gently because devfreq device is registered.
> > > Then devfreq checks device status, and reaches the state when
> > > counters 'get' function returns that they are not ready...
> > > 
> > > If that is a kind of 2-stage initialization, maybe we should add
> > > another 'check' in the exynos5_performance_counters_init() and call
> > > the devfreq_event_get_event() to make sure that we are ready to go,
> > > otherwise return ret from that function (which is probably EPROBE_DEFER)
> > > and not register the devfreq device.
> > 
> > I've finally investigated this further and it turned out that the issue
> > is elsewhere. The $subject patch can be discarded, as it doesn't fix
> > anything. The -EPROBE_DEFER is properly returned by
> > exynos5_performance_counters_init(), which redirects exynos5_dmc_probe()
> > to remove_clocks label. This causes disabling mout_bpll/fout_bpll clocks
> > what in turn *sometimes* causes boot hang. This random behavior mislead
> > me that the $subject patch fixes the issue, but then longer tests
> > revealed that it didn't change anything.
> 
> Really good investigation, great work Marek!
> 
> > 
> > It looks that the proper fix would be to keep fout_bpll enabled all the
> > time.
> 
> Yes, I agree. I am looking for your next patch to test it then.

Hi all,

Is the patch still useful then? Shall I apply it?

Best regards,
Krzysztof