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Fri, 10 Jul 2026 12:14:38 -0700 (PDT) X-Received: by 2002:a05:6a21:6e96:b0:3bf:b523:2aed with SMTP id adf61e73a8af0-3c1100383fcmr321970637.8.1783710878257; Fri, 10 Jul 2026 12:14:38 -0700 (PDT) Received: from localhost ([50.35.46.84]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-311747f5975sm40574288eec.4.2026.07.10.12.14.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Jul 2026 12:14:37 -0700 (PDT) Date: Fri, 10 Jul 2026 12:14:33 -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 , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 13/16] arm_mpam: prepare mon_sel locking for MPAM-Fb Message-ID: <20260710121433.00001ad6@oss.qualcomm.com> In-Reply-To: <20260710144520.917375-14-andre.przywara@arm.com> References: <20260710144520.917375-1-andre.przywara@arm.com> <20260710144520.917375-14-andre.przywara@arm.com> Organization: Qualcomm X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Authority-Analysis: v=2.4 cv=JJYLdcKb c=1 sm=1 tr=0 ts=6a51449f cx=c_pps a=m5Vt/hrsBiPMCU0y4gIsQw==:117 a=qC1CW/w66vtJz1P9yTJxNA==:17 a=kj9zAlcOel0A:10 a=RAioF0-LDSMA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yOCtJkima9RkubShWh1s:22 a=7CQSdrXTAAAA:8 a=TWr3UOjz1xACnXJDHjEA:9 a=CjuIK1q_8ugA:10 a=IoOABgeZipijB_acs4fv:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-ORIG-GUID: HRi-4T3XXG52-GlrAFDeIIYQzMzUMUkC X-Proofpoint-Spam-Info: AW1haW4tMjYwNzEwMDE5MyBTYWx0ZWRfX6e3fgoq67xxM LtmezvPqPJzWwQ2ZcYeIlXngCNgC4Cv+PIbG4HhAykfAjEQq/lTV9CAQpuVynL2mk1rcVMT0vaY AxvhRpSyzc/uUcB27Cy452q0VA6MMfM= X-Proofpoint-GUID: HRi-4T3XXG52-GlrAFDeIIYQzMzUMUkC X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzEwMDE5MyBTYWx0ZWRfX6D5++PAdoiLC +LQ4+ZCj/TQFHWXwop6Ba5NADcCdZjIpHFsPUwQZoVos3VHCy74GA1E5bE7hWiU0XcWuQUEoU1A 8JgHPaet2HseI+4ekQ+BB3TNuwMQGMxLASmiTSMjiw39axnc/usupVB3L75N5aZlMX74l9ELG1z iXjT7EVDVHAIZNsq8KqMamiTEL3SI5PpPF7gvGm/9jpDGH6EmJJZfG76RhbnQIq+6dWWKkJOCpf wtnP0CdY/wA97ib2bmK8Qph/C07Hq1Mt8YHHS1N35mk6Sw/7zY5mqIuxpr1srnQKXOeNY894QHC vYVP3CbtiaMJYLLfJiypgk5o7OlCgU5WIz3QSvVsyxWFh5apItOR69OHOr4P/YQxrD6ub7UsaEZ OQUXTzgn1Ao84eUaH+1IY5UsGI6YvoEikrX2W/R5lNcssGVQmoK3WfMqcdOFHqROahQj0DP7+hh Mrr4xQGiOYbvfOVNxNQ== 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=2026-07-10_05,2026-07-10_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 spamscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607100193 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260710_121440_541586_74A154D3 X-CRM114-Status: GOOD ( 24.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 10 Jul 2026 16:45:17 +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 MSC are not accesible from every CPU. This makes an irqsave > spinlock the obvious lock to protect these registers. On systems with SCMI > mailboxes it must be able to sleep, meaning a mutex must be used. The > SCMI platforms can't support an overflow interrupt. > Clearly these two 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. > > Signed-off-by: Andre Przywara I've not been paying attention to this topic, so I might come back with some more feedback after I've had time to think about it a bit! So trivial stuff only for now. > > static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc) > { > raw_spin_lock_init(&msc->_mon_sel_lock); > + mutex_init(&msc->mon_sel_mutex); I'm not that fussed, but maybe add a call to mutex_destroy(). Most likely it'll never help catch anything in this code though.. > } > > /* Bits for mpam features bitmaps */