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Date:   Thu, 16 May 2019 17:02:52 +0200
From:   Maxime Ripard <maxime.ripard@bootlin.com>
To:     Yangtao Li <tiny.windzz@gmail.com>, mark.rutland@arm.com,
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Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6
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Hi,

On Sun, May 12, 2019 at 11:41:28PM +0200, Ond=C5=99ej Jirman wrote:
> > > +static int tsens_get_temp(void *data, int *temp)
> > > +{
> > > +	struct tsensor *s =3D data;
> > > +	struct tsens_device *tmdev =3D s->tmdev;
> > > +	int val;
> > > +
> > > +	regmap_read(tmdev->regmap, tmdev->chip->temp_data_base +
> > > +		    0x4 * s->id, &val);
> > > +
> > > +	if (unlikely(val =3D=3D 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 =3D (-2794) * -67 =3D 187198
>
> 187=C2=B0C 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?

Maxime

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

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