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Date:   Fri, 17 May 2019 09:31:51 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Frank Lee <tiny.windzz@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        catalin.marinas@....com, will.deacon@....com,
        bjorn.andersson@...aro.org,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        paulmck@...ux.ibm.com, stefan.wahren@...e.com,
        Linux PM <linux-pm@...r.kernel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Andy Gross <andy.gross@...aro.org>, rui.zhang@...el.com,
        devicetree@...r.kernel.org, marc.w.gonzalez@...e.fr,
        Eduardo Valentin <edubezval@...il.com>,
        enric.balletbo@...labora.com, robh+dt@...nel.org,
        Jonathan.Cameron@...wei.com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        olof@...om.net, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6

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?

Maxime

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

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