Re: [PATCH] tty: max310x: work around regmap->regcache data corruption

[Jan Kundrát]

On pátek 1. prosince 2023 18:02:32 CET, Andy Shevchenko wrote:
> On Fri, Dec 1, 2023 at 6:21 PM Mark Brown <broonie@xxxxxxxxxx> wrote:
> > On Fri, Dec 01, 2023 at 03:51:51PM +0100, Jan Kundrát wrote:
> >
> > > The TL;DR summary is that the regmap_noinc_write spills over the data
> > > that are correctly written to the HW also to the following registers in
> > > the regcache. As a result, regcache then contains user-controlled
> > > garbage which will be used later for bit updates on unrelated registers.
> >
> > > I was investigating a regression that happened somewhere between 5.12.4
> > > (plus 14 of our patches) and v6.5.9 (plus 7 of our patches). Our
> >
> > Can you reproduce this with current kernels?  That's not even an up to
> > date v6.5 - we're up to v6.5.13 now from the looks of things including
> > one upstream fix that looks potentially relevant.
>
> Indeed, the 984a4afdc87a ("regmap: prevent noinc writes from
> clobbering cache") seems quite relevant.

Thank you, Andy, this is indeed the real fix.

Sorry that I missed it, Mark. I spent many days on this one over a longer 
period of time, so I haven't noticed that a fix was merged in the 
meanwhile. I was just very happy that I debugged something which looked 
like a real puzzle at the beginning :).

Cheers,
Jan