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Fri, 10 Apr 2026 01:45:23 -0700 (PDT) Received: from [192.168.1.3] ([185.48.77.170]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d63e5d85fsm4969913f8f.36.2026.04.10.01.45.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Apr 2026 01:45:23 -0700 (PDT) Message-ID: <8c0bf2f2-c577-4c8a-87b2-1488635185b3@linaro.org> Date: Fri, 10 Apr 2026 09:45:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 17/20] coresight: trbe: Save and restore state across CPU low power state To: Leo Yan Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, Suzuki K Poulose , Mike Leach , Yeoreum Yun , Mark Rutland , Will Deacon , Yabin Cui , Keita Morisaki , Yuanfang Zhang , Greg Kroah-Hartman , Alexander Shishkin , Tamas Petz , Thomas Gleixner , Peter Zijlstra References: <20260405-arm_coresight_path_power_management_improvement-v10-0-13e94754a8be@arm.com> <20260405-arm_coresight_path_power_management_improvement-v10-17-13e94754a8be@arm.com> <20260409155433.GV356832@e132581.arm.com> Content-Language: en-US From: James Clark In-Reply-To: <20260409155433.GV356832@e132581.arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260410_014525_733221_DE359239 X-CRM114-Status: GOOD ( 17.44 ) 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 09/04/2026 4:54 pm, Leo Yan wrote: > On Thu, Apr 09, 2026 at 11:52:06AM +0100, James Clark wrote: >> On 05/04/2026 4:02 pm, Leo Yan wrote: >>> From: Yabin Cui >>> >>> TRBE context can be lost when a CPU enters low power states. If a trace >>> source is restored while TRBE is not, tracing may run without an active >>> sink, which can lead to hangs on some devices (e.g., Pixel 9). >> >> Can't this still happen if saving the source times out on "wait for >> TRCSTATR.IDLE to go up"? >> >> That would make coresight_pm_save() exit early, not saving the active TRBE >> state. Then when coresight_pm_restore() is called it restores a stale >> inactive sink, then enables the source again which is the state that can >> hang. > > Hmm... I don't expect this to happen anyway. > > If CPU PM enter fails and returns an error, it will bail out early of > the idle flow and the CPU will not proceed entering low power states; > therefore, the restore flow does not exist. > > Thanks, > Leo Ah ok I missed that that was how it behaved. I didn't realise that an error here would prevent the restore from being called. That makes my other comments redundant as well then.