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

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Message-ID: <430727d2-7e88-4de2-97ab-e841656d7915@cesnet.cz>
Date:   Sat, 02 Dec 2023 11:29:15 +0100
From:   Jan Kundrát <jan.kundrat@...net.cz>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Cosmin Tanislav <cosmin.tanislav@...log.com>,
        <linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: max310x: work around regmap->regcache data corruption

On pátek 1. prosince 2023 18:02:32 CET, Andy Shevchenko wrote:
> On Fri, Dec 1, 2023 at 6:21 PM Mark Brown <broonie@...nel.org> 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