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Date:   Thu, 16 May 2019 19:36:49 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Yangtao Li <tiny.windzz@...il.com>, mark.rutland@....com,
        daniel.lezcano@...aro.org, catalin.marinas@....com,
        will.deacon@....com, bjorn.andersson@...aro.org,
        mchehab+samsung@...nel.org, paulmck@...ux.ibm.com,
        stefan.wahren@...e.com, linux-pm@...r.kernel.org, wens@...e.org,
        jagan@...rulasolutions.com, andy.gross@...aro.org,
        rui.zhang@...el.com, devicetree@...r.kernel.org,
        marc.w.gonzalez@...e.fr, edubezval@...il.com,
        enric.balletbo@...labora.com, robh+dt@...nel.org,
        Jonathan.Cameron@...wei.com, linux-arm-kernel@...ts.infradead.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        olof@...om.net, davem@...emloft.net
Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6

Hello Maxime,

On Thu, May 16, 2019 at 05:02:52PM +0200, Maxime Ripard wrote:
> Hi,
> 
> On Sun, May 12, 2019 at 11:41:28PM +0200, Ondřej Jirman wrote:
> > > > +static int tsens_get_temp(void *data, int *temp)
> > > > +{
> > > > +	struct tsensor *s = data;
> > > > +	struct tsens_device *tmdev = s->tmdev;
> > > > +	int val;
> > > > +
> > > > +	regmap_read(tmdev->regmap, tmdev->chip->temp_data_base +
> > > > +		    0x4 * s->id, &val);
> > > > +
> > > > +	if (unlikely(val == 0))
> > > > +		return -EBUSY;
> > >
> > > I'm not sure why a val equals to 0 would be associated with EBUSY?
> >
> > Thermal zone driver can (will) call get_temp before we got the
> > first interrupt and the thermal data. In that case val will be 0.
> >
> > Resulting in:
> >
> >  (val + offset) * scale = (-2794) * -67 = 187198
> >
> > 187°C and immediate shutdown during boot - based on cirtical
> > temperature being reached.
> >
> > Busy here means, get_temp does not yet have data. Thermal zone
> > driver just reports any error to dmesg output.
> 
> Ah, that makes sense.
> 
> I guess if we're switching to an interrupt-based driver, then we can
> just use a waitqueue, or is get_temp supposed to be atomic?

I'm not entirely sure, because I might have inadverently used a combination of
interrupt and polling when testing this. It may be that if we set polling-delay
to 0 in dts, that tz core will not try to call get_temp prematurely at all, and
will simply wait for temperature update from the interrupt.

I guess this needs to be tested/checked in tz code.

regards,
	o.

> Maxime
> 
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com



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