linux-kernel - Re: [PATCH v4] i2c: designware: Fix corrupted memory seen in the ISR

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Message-ID: <ZVGB0ul4MYIdLaWX@shikoro>
Date:   Sun, 12 Nov 2023 20:54:26 -0500
From:   Wolfram Sang <wsa@...nel.org>
To:     Jan Bottorff <janb@...amperecomputing.com>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        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>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] i2c: designware: Fix corrupted memory seen in the ISR

On Thu, Nov 09, 2023 at 03:19:27AM +0000, Jan Bottorff wrote:
> When running on a many core ARM64 server, errors were
> happening in the ISR that looked like corrupted memory. These
> corruptions would fix themselves if small delays were inserted
> in the ISR. Errors reported by the driver included "i2c_designware
> APMC0D0F:00: i2c_dw_xfer_msg: invalid target address" and
> "i2c_designware APMC0D0F:00:controller timed out" during
> in-band IPMI SSIF stress tests.
> 
> The problem was determined to be memory writes in the driver were not
> becoming visible to all cores when execution rapidly shifted between
> cores, like when a register write immediately triggers an ISR.
> Processors with weak memory ordering, like ARM64, make no
> guarantees about the order normal memory writes become globally
> visible, unless barrier instructions are used to control ordering.
> 
> To solve this, regmap accessor functions configured by this driver
> were changed to use non-relaxed forms of the low-level register
> access functions, which include a barrier on platforms that require
> it. This assures memory writes before a controller register access are
> visible to all cores. The community concluded defaulting to correct
> operation outweighed defaulting to the small performance gains from
> using relaxed access functions. Being a low speed device added weight to
> this choice of default register access behavior.
> 
> Signed-off-by: Jan Bottorff <janb@...amperecomputing.com>

Applied to for-current, thanks!


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