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From: Adam Ford <aford173@gmail.com>
Date: Fri, 7 Jun 2024 13:01:12 -0500
Message-ID: <CAHCN7xLoJK+_=+ASL=P8x=E3ALY-Xw=+_Zg+q0Za32kgvm5iQA@mail.gmail.com>
Subject: Re: [PATCH v1] media: i2c: imx219: fix msr access command sequence
To: Conor Dooley <conor@kernel.org>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.com>, 
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>, linux-media@vger.kernel.org, 
	Conor Dooley <conor.dooley@microchip.com>, Sakari Ailus <sakari.ailus@linux.intel.com>, 
	Mauro Carvalho Chehab <mchehab@kernel.org>, Andrey Konovalov <andrey.konovalov@linaro.org>, 
	linux-kernel@vger.kernel.org, Naushir Patuck <naush@raspberrypi.com>
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On Fri, Jun 7, 2024 at 12:55=E2=80=AFPM Conor Dooley <conor@kernel.org> wro=
te:
>
> On Fri, Jun 07, 2024 at 06:29:49PM +0100, Dave Stevenson wrote:
>
> > > > ---
> > > > I got the report of this third hand, I don't have a device and can'=
t
> > > > test this. I do wonder why the RPis get away with the sequence that
> > > > seemingly doesn't work for the guy that reported this to me. My the=
ory
> > > > is either that they noticed the sequence was wrong while adding som=
e
> > > > other MSR access that is needed on this board while either cross
> > > > checking the values written or because the other MSR accesses didn'=
t
> > > > take effect.
> >
> > Did the change fix it for the reporter? We're using the driver with no
> > changes to the register settings cf mainline.
> > Why it works on the Pi but not on a Microchip board is likely to be
> > something quite subtle.

I have two different platforms which can use this sensor.  I can try
to test it this weekend and I'll report back my findings.

adam
>
> I've asked, maybe it turns out to just be the first of my suggestions,
> and they noticed it was not matching in passing. They did introduce two
> additional MSR accesses, both outside of the range documented in the
> datasheets I could find online. They did have explanations for what those
> undocumented MSRs did (0x5040 and 0x5041) in the mail I got, but given
> it's third hand info to me, I dunno if we have the datasheet etc. I'll
> try to find out some more next week.
>
> Thanks,
> Conor.