On Fri, May 17, 2019 at 3:32 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
>
> On Fri, May 17, 2019 at 02:10:47AM +0800, Frank Lee wrote:
> > > 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 think get_temp should not be bloacked.
>
> Why not?
Maybe, I am wrong. I also want to know if we should do this.
Yangtao
>
> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
