linux-kernel - Re: [PATCH v2 26/29] arm_mpam: Use long MBWU counters if supported

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Message-ID: <20250912142929.00003cff@huawei.com>
Date: Fri, 12 Sep 2025 14:29:29 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
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	Danilo Krummrich <dakr@...nel.org>, Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH v2 26/29] arm_mpam: Use long MBWU counters if supported

On Wed, 10 Sep 2025 20:43:06 +0000
James Morse <james.morse@....com> wrote:

> From: Rohit Mathew <rohit.mathew@....com>
> 
> If the 44 bit (long) or 63 bit (LWD) counters are detected on probing
> the RIS, use long/LWD counter instead of the regular 31 bit mbwu
> counter.
> 
> Only 32bit accesses to the MSC are required to be supported by the
> spec, but these registers are 64bits. The lower half may overflow
> into the higher half between two 32bit reads. To avoid this, use
> a helper that reads the top half multiple times to check for overflow.
> 
> Signed-off-by: Rohit Mathew <rohit.mathew@....com>
> [morse: merged multiple patches from Rohit]
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>