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Date:   Fri, 24 Aug 2018 21:59:21 +0200
From:   Emmanuel Vadot <manu@bidouilliste.com>
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Emmanuel Vadot <manu@freebsd.org>,
        Chen-Yu Tsai <wens@csie.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        Zhang Rui <rui.zhang@intel.com>, devicetree@vger.kernel.org
Subject: Re: [PATCH 1/7] dt-bindings: Add DT bindings documentation for
 Allwinner Thermal Sensor Controller
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 Hi,

On Fri, 24 Aug 2018 16:58:40 +0200
Maxime Ripard <maxime.ripard@bootlin.com> wrote:

> Hi,
> 
> On Mon, Aug 20, 2018 at 04:27:15PM +0200, Emmanuel Vadot wrote:
> > On Mon, 20 Aug 2018 16:07:37 +0200
> > Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > 
> > > On Mon, Aug 20, 2018 at 07:41:22AM -0600, Rob Herring wrote:
> > > > On Mon, Aug 20, 2018 at 5:17 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > > >
> > > > > On Sat, Aug 04, 2018 at 09:03:49AM +0200, Emmanuel Vadot wrote:
> > > > > > This patch adds documentation for Device-Tree bindings for the Allwinner
> > > > > > Thermal Sensor Controller found on the H3, H5 and A64 SoCs
> > > > > >
> > > > > > Signed-off-by: Emmanuel Vadot <manu@freebsd.org>
> > > > >
> > > > > I'm not going to merge a binding for a device that doesn't have any
> > > > > driver implemented at the moment in Linux.
> > > > 
> > > > I'll take it then. Linux is not the only DT client.
> > > 
> > > Then don't complain if we ever have to break the ABI. We never tested
> > > that hardware, never had any code running on it, and it *will* cause
> > > some issues. For example, the calibration data have never been used
> > > and how they should be represented have never been described, since no
> > > one ever actually tried to use it.
> > > 
> > > And sure, Linux is not the only DT client. Just like FreeBSD isn't.
> > 
> >  What kind of data would you need for me to make things better ?
> >  We have the driver in FreeBSD for almost two years now, whne I started
> > to see how to upstream it I noticed a lot of problems and spent 4 or 5
> > days to try on all the SoCs mentionned in the serie, the only SoC I
> > didn't include it the A83T as for some reason I couldn't make the
> > driver work.
> 
> Do you have a link to that driver? 

 https://github.com/freebsd/freebsd/blob/master/sys/arm/allwinner/aw_thermal.c

> How and how much did you test it?

 Using a cheap IR thermometer as it's all I can afford.
 Then running multiples cpufreq-a53 process and comparing the result.
 Did the same without using the calibration data, result where closer
when I used them.

> Are you using the calibration data stored in the SID?

 Yes, which is why the serie contain the nvmem cell for the SID.

> 
> > I just hope that you understand that we cannot wait for Linux to
> > have a driver to have some bindings.
> 
> Just like I'm sure you can understand that just merging the DT bits
> without testing anything caused some troubles in the past, and I don't
> want to discover it in a year from now.

 I do, I don't like wrong DT info as much as you do I think. I had
the unfortunate event to find that the sun4i-a10-timer compatible used
in every soc is plain wrong for !A10 and !A13, patches comming soon.
 I want those bits merged but I also want that they reflect reality,
this is not a hard driver to do, NetBSD also have one I think, maybe
OpenBSD do to.

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


-- 
Emmanuel Vadot <manu@bidouilliste.com> <manu@freebsd.org>