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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb392b15f0sm33297415ad.73.2026.11.02.14.30.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Nov 2026 14:30:51 -0800 (PST) Message-ID: <5ea2dfe0-7d95-4ab6-a17e-33e3aaac38d6@redhat.com> Date: Tue, 3 Nov 2026 08:30:46 +1000 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm_mpam: avoid hour-long timeout on invalid ACPI table entry To: Andre Przywara , James Morse , Ben Horgan Cc: Reinette Chatre , Fenghua Yu , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20261102112748.3458012-1-andre.przywara@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20261102112748.3458012-1-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/2/26 9:27 PM, Andre Przywara wrote: > The ACPI PCCT table contains a "nominal latency" field for the expected > maximum time it takes to handle a command in the PCC mailbox. > The generic ACPI code reads this value, but leaves the handling to the > protocol users. > > For MPAM-Fb based MSC signalling, we use a value derived from that number > as the mailbox timeout. However if the ACPI table leaves this entry at 0, > the mailbox timeout code interprets this as "forever", and waits for one > hour. > > Avoid that lengthy timeout and just add one microsecond to the read value, > to come up with a non-zero result in any case. > > Found by Sashiko. > > Fixes: cb351e3f304b ("arm_mpam: detect and enable MPAM-Fb PCC support") > Signed-off-by: Andre Przywara > --- > drivers/resctrl/mpam_devices.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > Reviewed-by: Gavin Shan