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[103.229.18.19]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb3928f933sm40414795ad.58.2026.11.03.04.59.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2026 04:59:49 -0800 (PST) Message-ID: <72d9d2db-5cee-457f-ab03-0d166a84a49c@oss.qualcomm.com> Date: Tue, 3 Nov 2026 18:29:45 +0530 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: Srivathsa L Rao In-Reply-To: <20261102112748.3458012-1-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-ORIG-GUID: tcCz7E3HHYqTu_5FrHorV33HVvI7Qygh X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAzMDA1MSBTYWx0ZWRfXwoRis48Nn8C9 oNrQQd0G8vYZS6ik/fOJiGKmveyuPMlRg+8Fyn4t2vn7OYj5qyxPjtuk+/mUKcNkB0wWS009u7l 00AUV/klKhQUCBdUKvBFFLt9ZXru+Av8i/z9O6f22cMzxuxd4w6+IIQFqE5xSMWd7d83YzrQnBX s1+SNGK9xHNW2s5wRDdBuRL0DGfazTdamxmjTMR1YOvlHJoQK22Ud/BpZ0WU8r9Lt/GaYDnF/AN hPfafBdQG8gwx+TQh7abMyWPD7gM7HSSQ8IhHzRvmrNIbITXD5gLH+u/K1LHbrRQv3bCS9GXqws M01tOoFa1oh+5X7OA7L1iB0KdFbq/WniM6DIp2teqMW8oTXz+MH5RcdiyJtVfSOzWX4Rf2kGL1/ zTsrq23+mcGJ1RiSmfnjR/4jkuVR3id9WQItmUKjgtbkDI2eeybzkUop/R4uRW1+4nvCn2ShOd1 7k62sfRrPmu5/2kNJAw== X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAzMDA1MSBTYWx0ZWRfXz831o7JA8V6U qaADzRLv0eZ70CuajqYpY+EQtE6l5nCO8MoLp175TTAYP3Q5ZmiiS/Al4t7f40oz7L4wQ0t0pe2 yH4AIRzK0Upv8yuD5L4NzUdgFyHt8UY= X-Proofpoint-GUID: tcCz7E3HHYqTu_5FrHorV33HVvI7Qygh X-Authority-Analysis: v=2.4 cv=NZlzRGD4 c=1 sm=1 tr=0 ts=6ae9dac7 cx=c_pps a=JL+w9abYAAE89/QcEU+0QA==:117 a=Ou0eQOY4+eZoSc0qltEV5Q==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=ZpdpYltYx_vBUK5n70dp:22 a=7CQSdrXTAAAA:8 a=EUspDBNiAAAA:8 a=xQjQ7c2AriHHlxExpPEA:9 a=QEXdDO2ut3YA:10 a=324X-CrmTo6CU4MGRt3R:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-03_02,2026-11-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 phishscore=0 priorityscore=1501 suspectscore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611030051 Hi Andre, On 11/2/2026 4:57 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(-) > > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c > index c067b6d57d71e..fb596ed19a648 100644 > --- a/drivers/resctrl/mpam_devices.c > +++ b/drivers/resctrl/mpam_devices.c > @@ -102,9 +102,9 @@ static struct mpam_pcc_chan *mpam_pcc_chan_get(struct device *dev, > /* > * Timeout based on the "nominal latency" in us, from the > * PCC ACPI table. tx_tout is in ms. > - * Add some margin here to be on the safe side. > + * Add some margin here to be on the safe side, and avoid using 0. > */ > - cur->pcc_cl.tx_tout = DIV_ROUND_UP(cur->pcc_chan->latency * 5, 1000); > + cur->pcc_cl.tx_tout = DIV_ROUND_UP((cur->pcc_chan->latency + 1) * 5, 1000); Would an explicit floor, e.g max(DIV_ROUND_UP(latency * 5, 1000), MPAM_PCC_MIN_TIMEOUT_MS), with a comment, be better than "+ 1"? It also avoids the side effect on non-zero. Just a suggestion.> > mutex_init(&cur->pcc_chan_lock); > > > base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4 Reviewed-by: Srivathsa L Rao Best Regards, Srivathsa