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From:   Frank Lee <tiny.windzz@gmail.com>
Date:   Sat, 18 May 2019 01:19:54 +0800
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Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        catalin.marinas@arm.com, will.deacon@arm.com,
        bjorn.andersson@linaro.org,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        paulmck@linux.ibm.com, stefan.wahren@i2se.com,
        Linux PM <linux-pm@vger.kernel.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Andy Gross <andy.gross@linaro.org>, rui.zhang@intel.com,
        devicetree@vger.kernel.org, marc.w.gonzalez@free.fr,
        Eduardo Valentin <edubezval@gmail.com>,
        enric.balletbo@collabora.com, robh+dt@kernel.org,
        Jonathan.Cameron@huawei.com,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        olof@lixom.net, David Miller <davem@davemloft.net>
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On Fri, May 17, 2019 at 3:32 PM Maxime Ripard <maxime.ripard@bootlin.com> w=
rote:
>
> On Fri, May 17, 2019 at 02:10:47AM +0800, Frank Lee wrote:
> > > 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?
> >
> > 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