linux-kernel - Re: [PATCH] thermal: sun8i: Be loud when probe fails

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Message-ID: <20200708132924.r6f5id2evprhybec@core.my.home>
Date:   Wed, 8 Jul 2020 15:29:24 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     linux-sunxi@...glegroups.com,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Yangtao Li <tiny.windzz@...il.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Chen-Yu Tsai <wens@...e.org>,
        "open list:ALLWINNER THERMAL DRIVER" <linux-pm@...r.kernel.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal: sun8i: Be loud when probe fails

Hello Maxime,

On Wed, Jul 08, 2020 at 02:25:42PM +0200, Maxime Ripard wrote:
> Hi,
> 
> On Wed, Jul 08, 2020 at 12:55:27PM +0200, Ondrej Jirman wrote:
> > I noticed several mobile Linux distributions failing to enable the
> > thermal regulation correctly, because the kernel is silent
> > when thermal driver fails to probe. Add enough error reporting
> > to debug issues and warn users in case thermal sensor is failing
> > to probe.
> > 
> > Failing to notify users means, that SoC can easily overheat under
> > load.
> > 
> > Signed-off-by: Ondrej Jirman <megous@...ous.com>
> > ---
> >  drivers/thermal/sun8i_thermal.c | 55 ++++++++++++++++++++++++++-------
> >  1 file changed, 43 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/thermal/sun8i_thermal.c b/drivers/thermal/sun8i_thermal.c
> > index 74d73be16496..9065e79ae743 100644
> > --- a/drivers/thermal/sun8i_thermal.c
> > +++ b/drivers/thermal/sun8i_thermal.c
> > @@ -287,8 +287,12 @@ static int sun8i_ths_calibrate(struct ths_device *tmdev)
> >  
> >  	calcell = devm_nvmem_cell_get(dev, "calibration");
> >  	if (IS_ERR(calcell)) {
> > +		dev_err(dev, "Failed to get calibration nvmem cell (%ld)\n",
> > +			PTR_ERR(calcell));
> > +
> >  		if (PTR_ERR(calcell) == -EPROBE_DEFER)
> >  			return -EPROBE_DEFER;
> > +
> 
> The rest of the patch makes sense, but we should probably put the error
> message after the EPROBE_DEFER return so that we don't print any extra
> noise that isn't necessarily useful

I thought about that, but in this case this would have helped, see my other
e-mail. Though lack of "probe success" message may be enough for me, to
debug the issue, I'm not sure the user will notice that a message is missing, while
he'll surely notice if there's a flood of repeated EPROBE_DEFER messages.

And people run several distros for 3-4 months without anyone noticing any
issues and that thermal regulation doesn't work. So it seems that lack of a
success message is not enough.

Other solution may be to select CONFIG_NVMEM_SUNXI_SID if this driver
is enabled. That may get rid of this error scenario of waiting infinitely
for calibration data with EPROBE_DEFER. And other potential EPROBE_DEFER sources
will probably be quite visible even without this driver telling the user.
So this message may not be necessary in that case.

thank you and regards,
	o.

> Maxime