linux-kernel - Re: [PATCH v1] media: i2c: imx219: fix msr access command sequence

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Date: Fri, 7 Jun 2024 18:55:01 +0100
From: Conor Dooley <conor@...nel.org>
To: Dave Stevenson <dave.stevenson@...pberrypi.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org,
	Conor Dooley <conor.dooley@...rochip.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Adam Ford <aford173@...il.com>,
	Andrey Konovalov <andrey.konovalov@...aro.org>,
	linux-kernel@...r.kernel.org,
	Naushir Patuck <naush@...pberrypi.com>
Subject: Re: [PATCH v1] media: i2c: imx219: fix msr access command sequence

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 theory
> > > is either that they noticed the sequence was wrong while adding some
> > > 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'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.

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