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From:   =?iso-8859-1?Q?Jan_Kundr=E1t?= <jan.kundrat@cesnet.cz>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>,
        Mark Brown <broonie@kernel.org>
Cc:     Cosmin Tanislav <cosmin.tanislav@analog.com>,
        <linux-serial@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tty: max310x: work around regmap->regcache data =?iso-8859-1?Q?corruption?=
Date:   Sat, 02 Dec 2023 11:29:15 +0100
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On p=C3=A1tek 1. prosince 2023 18:02:32 CET, Andy Shevchenko wrote:
> On Fri, Dec 1, 2023 at 6:21=E2=80=AFPM Mark Brown <broonie@kernel.org> wrot=
e:
>> On Fri, Dec 01, 2023 at 03:51:51PM +0100, Jan Kundr=C3=A1t wrote:
>>=20
>>> 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.
>>=20
>>> 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
>>=20
>> 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=20
period of time, so I haven't noticed that a fix was merged in the=20
meanwhile. I was just very happy that I debugged something which looked=20
like a real puzzle at the beginning :).

Cheers,
Jan