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

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Message-ID: <20240610-wolverine-hanky-37cc8c409958@wendy>
Date: Mon, 10 Jun 2024 08:31:33 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
To: Conor Dooley <conor@...nel.org>
CC: Dave Stevenson <dave.stevenson@...pberrypi.com>, Laurent Pinchart
	<laurent.pinchart@...asonboard.com>, <linux-media@...r.kernel.org>, 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 06:55:01PM +0100, Conor Dooley wrote:
> 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.

Apparently it was the latter & they did need to fix the sequence to be
able to write the MSRs.

> 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.

Seemingly what those two additional MSRs do is under NDA so I would have
no way of justifying a patch to add them or the devicetree property
required to know whether or not the additional MSR writes is needed. :)


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