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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b2d4f25df6sm105647345ad.56.2026.04.12.22.45.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 12 Apr 2026 22:46:14 -0700 (PDT) Message-ID: <227b77b9-5232-4cff-b26a-458477e9eb32@oss.qualcomm.com> Date: Mon, 13 Apr 2026 13:45:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 16/20] coresight: Add PM callbacks for sink device To: Leo Yan , Suzuki K Poulose , Mike Leach , James Clark , Yeoreum Yun , Mark Rutland , Will Deacon , Yabin Cui , Keita Morisaki , Yuanfang Zhang , Greg Kroah-Hartman , Alexander Shishkin , Tamas Petz , Thomas Gleixner , Peter Zijlstra Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org References: <20260405-arm_coresight_path_power_management_improvement-v10-0-13e94754a8be@arm.com> <20260405-arm_coresight_path_power_management_improvement-v10-16-13e94754a8be@arm.com> Content-Language: en-US From: Jie Gan In-Reply-To: <20260405-arm_coresight_path_power_management_improvement-v10-16-13e94754a8be@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDEzMDA1MSBTYWx0ZWRfX6+VoCauaKSgW nm6HYVa5VXGZtHG6z7tpHT6zX3OO6qP1nMyiXczWoJesw0fgM8H+MTMtZhgRv9C3NypjUVMsryh bZv901txGE5XopKMETl8LHFW6d8oZkKu1wQ8wl9GCszya9BNWL+lKt92OIwaKhBLyDSmwED45EW 7ddFPkk/clNkjhtdwezFIslRFUQnjlDn3oDcNyuYu2HMtyQIMhhoDIj4rdW3nYfHlNAkBKBkPwO EnDAPQkV0KAz1STsxBcri5aCp/+Lfx0Xt14zGu2MPHveOtDtR0W/HvNDAFNHPpTYL+MwBhwmwR5 Nq3e2NVFb/m/GvohnfCPnXiXZ4wdewDhWmbuzMVYmfJXk/3Qnf8r0TQ+GSeXlNTaG80tmPQLRRx UXTipQ/xqMzxj/uVzSkH3HvKsbKTkgEAlN/Z7MTOPfDWGVLvyNESO4BKUrLelgCOhc3jw72emmd EDRCaXlqz12gPAN3n6g== X-Proofpoint-GUID: -P-o75XOZB7uDvw5OAaWAp_UKmLHspOa X-Authority-Analysis: v=2.4 cv=AofeGu9P c=1 sm=1 tr=0 ts=69dc8328 cx=c_pps a=JL+w9abYAAE89/QcEU+0QA==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=KKAkSRfTAAAA:8 a=7CQSdrXTAAAA:8 a=i0V9v3Km83Zjb9AMHTMA:9 a=QEXdDO2ut3YA:10 a=324X-CrmTo6CU4MGRt3R:22 a=cvBusfyB2V15izCimMoJ:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-ORIG-GUID: -P-o75XOZB7uDvw5OAaWAp_UKmLHspOa X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-13_02,2026-04-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 priorityscore=1501 clxscore=1015 impostorscore=0 suspectscore=0 malwarescore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604130051 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260412_224618_612704_B1E95850 X-CRM114-Status: GOOD ( 31.46 ) 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 4/5/2026 11:02 PM, Leo Yan wrote: > Unlike system level sinks, per-CPU sinks may lose power during CPU idle > states. Currently, this applies specifically to TRBE. This commit > invokes save and restore callbacks for the sink in the CPU PM notifier. > > If the sink provides PM callbacks but the source does not, this is > unsafe because the sink cannot be disabled safely unless the source > can also be controlled, so veto low power entry to avoid lockups. > > Tested-by: James Clark > Reviewed-by: Yeoreum Yun > Reviewed-by: James Clark > Signed-off-by: Leo Yan > --- > drivers/hwtracing/coresight/coresight-core.c | 46 ++++++++++++++++++++++++++-- > 1 file changed, 43 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c > index c1e8debc76aba7eb5ecf7efe2a3b9b8b3e11b10c..a918bf6398a932de30fe9b4947020cc4c1cfb2f7 100644 > --- a/drivers/hwtracing/coresight/coresight-core.c > +++ b/drivers/hwtracing/coresight/coresight-core.c > @@ -1736,14 +1736,15 @@ static void coresight_release_device_list(void) > /* Return: 1 if PM is required, 0 if skip, <0 on error */ > static int coresight_pm_check(struct coresight_path *path) > { > - struct coresight_device *source; > - bool source_has_cb; > + struct coresight_device *source, *sink; > + bool source_has_cb, sink_has_cb; > > if (!path) > return 0; > > source = coresight_get_source(path); > - if (!source) > + sink = coresight_get_sink(path); > + if (!source || !sink) > return 0; > > /* Don't save and restore if the source is inactive */ > @@ -1759,16 +1760,36 @@ static int coresight_pm_check(struct coresight_path *path) > if (source_has_cb) > return 1; > > + sink_has_cb = coresight_ops(sink)->pm_save_disable && > + coresight_ops(sink)->pm_restore_enable; > + /* > + * It is not permitted that the source has no callbacks while the sink > + * does, as the sink cannot be disabled without disabling the source, > + * which may lead to lockups. Alternatively, the ETM driver should > + * enable self-hosted PM mode at probe (see etm4_probe()). > + */ > + if (sink_has_cb) { > + pr_warn_once("coresight PM failed: source has no PM callbacks; " > + "cannot safely control sink\n"); > + return -EINVAL; > + } > + > return 0; > } > > static int coresight_pm_device_save(struct coresight_device *csdev) > { > + if (!csdev || !coresight_ops(csdev)->pm_save_disable) > + return 0; > + > return coresight_ops(csdev)->pm_save_disable(csdev); > } > > static void coresight_pm_device_restore(struct coresight_device *csdev) > { > + if (!csdev || !coresight_ops(csdev)->pm_restore_enable) > + return; > + > coresight_ops(csdev)->pm_restore_enable(csdev); > } > > @@ -1787,15 +1808,32 @@ static int coresight_pm_save(struct coresight_path *path) > to = list_prev_entry(coresight_path_last_node(path), link); > coresight_disable_path_from_to(path, from, to); > > + ret = coresight_pm_device_save(coresight_get_sink(path)); > + if (ret) > + goto sink_failed; > + > return 0; > + > +sink_failed: > + if (!coresight_enable_path_from_to(path, coresight_get_mode(source), > + from, to)) > + coresight_pm_device_restore(source); I have go through the history messages. I have a question about this point here: how can we handle the scenario if coresight_enable_path_from_to failed? It means we are never calling coresight_pm_device_restore for the ETM and leaving the ETM with OS lock state until CPU reset? Consider we are calling etm4_disable_hw with OS lock: etm4_disable_hw -> etm4_disable_trace_unit -> etm4x_wait_status (may timeout here?) Thanks, Jie > + > + pr_err("Failed in coresight PM save on CPU%d: %d\n", > + smp_processor_id(), ret); > + this_cpu_write(percpu_pm_failed, true); > + return ret; > } > > static void coresight_pm_restore(struct coresight_path *path) > { > struct coresight_device *source = coresight_get_source(path); > + struct coresight_device *sink = coresight_get_sink(path); > struct coresight_node *from, *to; > int ret; > > + coresight_pm_device_restore(sink); > + > from = coresight_path_first_node(path); > /* Up to the node before sink to avoid latency */ > to = list_prev_entry(coresight_path_last_node(path), link); > @@ -1808,6 +1846,8 @@ static void coresight_pm_restore(struct coresight_path *path) > return; > > path_failed: > + coresight_pm_device_save(sink); > + > pr_err("Failed in coresight PM restore on CPU%d: %d\n", > smp_processor_id(), ret); > >