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Subject: Re: [PATCH 1/7] iio: adc: sun4i-gpadc: rework for support multiple
 thermal sensor
From:   Icenowy Zheng <icenowy@aosc.io>
To:     Maxime Ripard <maxime.ripard@bootlin.com>,
        Jonathan Cameron <jic23@kernel.org>
Cc:     mark.rutland@arm.com, devicetree@vger.kernel.org, lars@metafoo.de,
        Yangtao Li <tiny.windzz@gmail.com>,
        linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
        wens@csie.org, robh+dt@kernel.org, pmeerw@pmeerw.net,
        knaack.h@gmx.de, lee.jones@linaro.org,
        linux-arm-kernel@lists.infradead.org
Date:   Tue, 07 May 2019 00:52:22 +0800
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在 2019-05-06一的 14:28 +0200，Maxime Ripard写道：
> Hi,
> 
> On Sun, May 05, 2019 at 04:22:15PM +0100, Jonathan Cameron wrote:
> > On Fri,  3 May 2019 03:28:07 -0400
> > Yangtao Li <tiny.windzz@gmail.com> wrote:
> > 
> > > For some SOCs, there are more than one thermal sensor, and there
> > > are
> > > currently four sensors on the A80. So we need to do some work in
> > > order
> > > to support multiple thermal sensors:
> > > 
> > >   1) add sensor_count in gpadc_data.
> > >   2) introduce sun4i_sensor_tzd in sun4i_gpadc_iio, to support
> > > multiple
> > >      thermal_zone_device and distinguish between different
> > > sensors.
> > >   3) modify read temperature and initialization function.
> > 
> > This comment doesn't mention the devm change. If it had it would
> > have
> > raised immediate alarm bells.
> > 
> > I'm also not keen on the web of pointers that this driver is
> > steadily
> > evolving.  I can't immediately see how to reduce that complexity
> > however.
> 
> So I might be responsible for that, and looking back, this has been a
> mistake.
> 
> This driver was initally put together to support a controller found
> in
> older (A10 up to A31) Allwinner SoCs. This controller had an ADC
> driver that could be operated as a touchscreen controller, and was
> providing a CPU temperature sensor and a general purpose ADC.
> 
> However, we already had a driver for that controller in drivers/input
> to report the CPU temperature, and the one in IIO was introduced to
> support the general purpose ADC (and the CPU temperature). The long
> term goal was to add the touchscreen feature as well eventually so
> that we could remove the one in drivers/input. That didn't happen.
> 
> At the same time, the Allwinner hardware slowly evolved to remove the
> touchscreen and ADC features, and only keep the CPU temperature
> readout. It then evolved further on to support multiple temperatures
> (for different clusters, the GPU, and so on).
> 
> So, today, we're in a situation where I was pushing everything into
> that IIO drivers since there was similiraties between all the
> generations, but the fact that we have to support so many odd cases
> (DT bindings compatibility, controllers with and without ADC, etc)
> that it becomes a real mess.
> 
> And that mess isn't really used by anybody, since we want to have the
> touchscreen.
> 
> There's only one SoC that is supported only by that driver, which is
> the A33 that only had a CPU temperature readout, and is still pretty
> similar to the latest SoC from Allwinner (that is supported by this
> series).
> 
> I guess, for everyone's sanity and in order to not stall this
> further,
> it would just be better to create an hwmon driver for the A33 (and
> onwards, including the H6) for the SoC that just have the temperature
> readout feature. And for the older SoC, we just keep the older driver
> under input/. Once the A33 is supported, we'll remove the driver in
> IIO (and the related bits in drivers/mfd).

I think a thermal driver is better.

Other SoCs' thermal sensor drivers are all thermal drivers.

> 
> Armbian already has a driver for that they never upstreamed iirc, so
> it might be a good starting point, and we would add the support for
> the H6. How does that sound?

I think the developer abandoned to upstream it because of the previous
problem ;-)

Maybe it can be taken and add A33&H6 support.

> 
> Sorry for wasting everybody's time on this.
> 
> Maxime
> 
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
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