linux-kernel - Re: [PATCH v2] i2c: designware: Fix corrupted memory seen in the ISR

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Message-ID: <ab57ba73-ce62-43fc-9cb1-d2db1bd13cd9@os.amperecomputing.com>
Date:   Mon, 30 Oct 2023 17:12:01 -0700
From:   Jan Bottorff <janb@...amperecomputing.com>
To:     Wolfram Sang <wsa@...nel.org>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Yann Sionneau <ysionneau@...rayinc.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Yann Sionneau <yann@...nneau.net>,
        Will Deacon <will@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jan Dabros <jsd@...ihalf.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: designware: Fix corrupted memory seen in the ISR

On 10/26/2023 4:18 AM, Wolfram Sang wrote:
> So, someone wants to come up with a patch to move to non-relaxed io
> accessors?
> 
Is the current thinking to just make writes to DW_IC_INTR_MASK use the 
non-relaxed variant or something more broad?

 From a safest functioning viewpoint, we talked about making all 
accessors default to non-relaxed variants. A couple of pretty good 
arguments from knowledgeable people favored this. I know there also was 
some concerns about potential performance impact this might have 
although the counter argument was this is a pretty low speed device so 
some extra cpu cycles on register accesses were not likely to degrade 
overall performance.

I could make the patch if we have consensus (or maintainers decision) on 
which way to go: 1) only writes to DW_IC_INTR_MASK are non-relaxed, 2) 
make all read/write accessors use the non-relaxed version.

I'm personally in camp #2, safety first, performance fine tuning later 
if needed. Latent missing barrier bugs are difficult and time consuming 
to find.

- Jan