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Thu, 30 Jul 2026 11:37:35 -0700 (PDT) X-Received: by 2002:a17:90a:dfcf:b0:380:f85c:94b4 with SMTP id 98e67ed59e1d1-38f9bda5a9cmr3056939a91.7.1785436654806; Thu, 30 Jul 2026 11:37:34 -0700 (PDT) Received: from localhost ([50.35.46.84]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-31504b10cdcsm24287056eec.3.2026.07.30.11.37.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 11:37:34 -0700 (PDT) Date: Thu, 30 Jul 2026 11:37:29 -0700 From: Jonathan Cameron To: Andre Przywara Cc: Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , "Rafael J . Wysocki" , Len Brown , James Morse , Ben Horgan , Reinette Chatre , Fenghua Yu , Jonathan Cameron , Srivathsa L Rao , Ganapatrao Kulkarni , Trilok Soni , Srinivas Ramana , Niyas Sait , Lee Trager , Ritwick Sharma , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 07/10] arm_mpam: prepare mon_sel locking for MPAM-Fb Message-ID: <20260730113729.000046c0@oss.qualcomm.com> In-Reply-To: <20260730152539.2712312-8-andre.przywara@arm.com> References: <20260730152539.2712312-1-andre.przywara@arm.com> <20260730152539.2712312-8-andre.przywara@arm.com> Organization: Qualcomm X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Authority-Analysis: v=2.4 cv=V4tNF+ni c=1 sm=1 tr=0 ts=6a6b99f0 cx=c_pps a=RP+M6JBNLl+fLTcSJhASfg==:117 a=qC1CW/w66vtJz1P9yTJxNA==:17 a=kj9zAlcOel0A:10 a=RAioF0-LDSMA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=ZpdpYltYx_vBUK5n70dp:22 a=7CQSdrXTAAAA:8 a=EUspDBNiAAAA:8 a=TWr3UOjz1xACnXJDHjEA:9 a=CjuIK1q_8ugA:10 a=iS9zxrgQBfv6-_F4QbHw:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-GUID: g3p96Pb7hUu11-gwpRz2dsecdPVKHB4F X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzMwMDEzNyBTYWx0ZWRfX4vqpSCk3Jykd 5orONyC8rgPakmYmZy+zZua1wEDKDoGabibR+dRizAyAklH2D4g6oOq2GQcMgZDhAWZkJCvW0Ho HmfOS8w8uO2bGT77uw+pJwrDBg5QQbzEFW+jvBEL9muiS6sVcEj5dY1SYTbwOJnNJfDE9S/tOq7 pQrnhrauYdSEI5SbaDcqlpBZzQThSr4/4WfBWGRZV2fjOjcXL8GXENG+Psv571Xk32diOHducys vg+J8cMLz7V0x/CJznjZC2pupdAS8cuk27Gkj6ck8QCgQDSvduUFa4A7gi33C2GDXG9Wn/3hAgX +OB6kdQ6BZZ6Tx/smim71DGfGZUGpfeMoocFwKXdj6sflSB8CdJ5xLPXaZMdBgJcfMNLjZGMziw 4utUKVF+QUygOGLafOgNvXeOg+7zHpLIKl0V6SjjTVaHi/8wka3LEg6BHF68UEdr+r/0NqDneyd MrpoE8pOGSI9pRfGBVQ== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzMwMDEzNyBTYWx0ZWRfXwHPM9OAkhzy3 E/WpYM3+clRBs+CKGem83bY/yTA9S0pDdQVAkDri3FtdqWi/WIAHtLxRJnPM0A5F2yOj72p/vli lW0hq8VYARppeMwu94Ea4WDPVv2SWvk= X-Proofpoint-ORIG-GUID: g3p96Pb7hUu11-gwpRz2dsecdPVKHB4F X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-30_05,2026-07-30_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 bulkscore=0 impostorscore=0 suspectscore=0 phishscore=0 adultscore=0 spamscore=0 priorityscore=1501 lowpriorityscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607300137 On Thu, 30 Jul 2026 17:25:36 +0200 Andre Przywara wrote: > The MSC MON_SEL register needs to be accessed from hardirq for the overflow > interrupt, and when taking an IPI to access these registers on platforms > where MSCs are not accesible from every CPU. This makes an irqsave > spinlock the obvious lock to protect these registers. On systems with > MPAM-Fb mailbox MSC access it must be able to sleep, meaning a mutex must > be used. So MPAM-Fb platforms cannot support an overflow interrupt easily. > Clearly these two methods can't exist for one MSC at the same time. > > Change the mon_sel locking wrapper function to only use a spinlock when > the MSC is accessed directly via MMIO. In case of MPAM-Fb, we use a > mutex, but only if we are in a sleepable context. If that's not the > case, we return an error. This should not happen, as MPAM-Fb by design > does not require an MSC access to happen from a specific CPU, so there > is no need for any IPIs or preemption disabling to satisfy CPU > constraints. And since overflow interrupts are not supported at the moment > anyway, we also wouldn't meet the other case. > Bailing out early is already happening in rare occasions today. > > Signed-off-by: Andre Przywara Not sure why I didn't tag this one before. Reviewed-by: Jonathan Cameron