Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6

[Frank Lee]

On Thu, May 16, 2019 at 11:03 PM Maxime Ripard
<maxime.ripard@xxxxxxxxxxx> wrote:
>
> Hi,
>
> On Sun, May 12, 2019 at 11:41:28PM +0200, OndÅej 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
> >
> > 187ÂC 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 think get_temp should not be bloacked.

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