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

From: Maxime Ripard <maxime.ripard@bootlin.com>
To: Frank Lee <tiny.windzz@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	catalin.marinas@arm.com, will.deacon@arm.com,
	bjorn.andersson@linaro.org, marc.w.gonzalez@free.fr,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	paulmck@linux.ibm.com, stefan.wahren@i2se.com,
	Daniel Lezcano <daniel.lezcano@linaro.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,
	Linux PM <linux-pm@vger.kernel.org>,
	Eduardo Valentin <edubezval@gmail.com>,
	olof@lixom.net, 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>,
	enric.balletbo@collabora.com, David Miller <davem@davemloft.net>
Subject: Re: [PATCH 2/3] thermal: sun50i: add thermal driver for h6
Date: Fri, 17 May 2019 09:31:51 +0200	[thread overview]
Message-ID: <20190517073151.mz6hcmzubk7iqfre@flea> (raw)
In-Reply-To: <CAEExFWu-T2mGQ9Teo7TQOcJsEzXi_dB=S8CFv7MiwHyu5z4-ow@mail.gmail.com>

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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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