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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c92bcc91f6dsm7072662a12.27.2026.06.28.22.55.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 28 Jun 2026 22:56:04 -0700 (PDT) Message-ID: <1714ad84-18cf-48d4-973d-b5e454d27c6c@oss.qualcomm.com> Date: Mon, 29 Jun 2026 13:55:56 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/12] coresight: Add CPU cluster funnel/replicator/tmc support To: "Maulik Shah (mkshah)" , Sudeep Holla , ulfh@kernel.org, Suzuki K Poulose , Leo Yan Cc: Mike Leach , James Clark , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Mathieu Poirier , Alexander Shishkin , Bjorn Andersson , Konrad Dybcio , kernel@oss.qualcomm.com, coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Jie Gan References: <20251218-cpu_cluster_component_pm-v2-0-2335a6ae62a0@oss.qualcomm.com> <20251218-careful-ruby-wildebeest-a8babd@sudeepholla> <20251219-hysterical-sparkling-meerkat-59c5eb@sudeepholla> <11a01108-63da-4317-a547-5977a469a7dc@oss.qualcomm.com> From: Yuanfang Zhang In-Reply-To: <11a01108-63da-4317-a547-5977a469a7dc@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjI5MDA0OCBTYWx0ZWRfX7+Zi4J934btO 17zZWTnzsXGGtZTx77bXyuqA8AzBr7FyxXD3g+f3NSldcH1XWxNnRIPWxtry0rpiZhDJQYmuQu+ p2VZh0MzZ1Org+afu6/6bWHV0vU9HKIbyFfgeCd13riyxVY2N2D2m3IWJZq4FUyfW13aNtxyXHT BP4DgAGVomfuIBv7XUCG3RcI+8r124gxamu1j3DaptDCTa/eFhh4ut162SrxVDFiPax4Silquyw MK9cl7W2dFjVPSaT1r70594AUDxXGRsYFpWswptJXTMlzVhdsn6UpJIGSRRK1Vs+LBn+f5LJxJ+ +ECc8QnLVczBwAm4Qgpnasekd7IKHTnr3NfpIOV05/ulteJmgIqkSmTpR3eQ/d6zXZWyLM2by/Y tlV21qq2j8enbL4KnVG3ulhH2qmMGSPTS7AO1njMY6+R+M1QXJ+OJdxZcHsNXKRUXNkS8kEBfB2 geFphKslv9voW1dfVCA== X-Proofpoint-GUID: z6FNNP9wL_vsBxiRvNRaRj2hRTW8QSPY X-Proofpoint-Spam-Info: AW1haW4tMjYwNjI5MDA0OCBTYWx0ZWRfXw3+xr5VsFB1l R/tk9TI40XTYUi+14GMG5u+xzBMNt2kwj1RSYCV7tV/UdWkKWRt6OzwUdzzHDZj39dDuu2jPzyf LrwjRZ2l5ggNYVLNU+zK4WgLbAh0qvY= X-Proofpoint-ORIG-GUID: z6FNNP9wL_vsBxiRvNRaRj2hRTW8QSPY X-Authority-Analysis: v=2.4 cv=BdnoFLt2 c=1 sm=1 tr=0 ts=6a4208f5 cx=c_pps a=RP+M6JBNLl+fLTcSJhASfg==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=YMgV9FUhrdKAYTUUvYB2:22 a=7CQSdrXTAAAA:8 a=-HkNxc-VA3X1G4HRPRMA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=iS9zxrgQBfv6-_F4QbHw:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-29_01,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 clxscore=1011 suspectscore=0 bulkscore=0 impostorscore=0 spamscore=0 lowpriorityscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606290048 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260628_225607_040012_B2900D67 X-CRM114-Status: GOOD ( 51.85 ) 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 Hi Sudeep & Suzuki, Gentle reminder on this patch. Any feedback would be appreciated. Thanks, Yuanfang. On 5/25/2026 9:17 PM, Maulik Shah (mkshah) wrote: > > > On 12/19/2025 3:51 PM, Sudeep Holla wrote: >> On Fri, Dec 19, 2025 at 10:13:14AM +0800, yuanfang zhang wrote: >>> >>> >>> On 12/18/2025 7:33 PM, Sudeep Holla wrote: >>>> On Thu, Dec 18, 2025 at 12:09:40AM -0800, Yuanfang Zhang wrote: >>>>> This patch series adds support for CoreSight components local to CPU clusters, >>>>> including funnel, replicator, and TMC, which reside within CPU cluster power >>>>> domains. These components require special handling due to power domain >>>>> constraints. >>>>> >>>> >>>> Could you clarify why PSCI-based power domains associated with clusters in >>>> domain-idle-states cannot address these requirements, given that PSCI CPU-idle >>>> OSI mode was originally intended to support them? My understanding of this >>>> patch series is that OSI mode is unable to do so, which, if accurate, appears >>>> to be a flaw that should be corrected. >>> >>> It is due to the particular characteristics of the CPU cluster power >>> domain.Runtime PM for CPU devices works little different, it is mostly used >>> to manage hierarchicalCPU topology (PSCI OSI mode) to talk with genpd >>> framework to manage the last CPU handling in cluster. >> >> That is indeed the intended design. Could you clarify which specific >> characteristics differentiate it here? > > Sorry for coming very late on this. > > This series is intended to handle coresight components which resides within CPU cluster. > For the cases where cluster is in deepest idle low power mode or all CPUs belonging to cluster > are hotplugged off, access to coresight components can not be done. > > The implementation tried to address in two parts, > 1. Using cluster power-domain to know which coresight component belongs to which cluster/CPUs > 2. Schedule the task on intended cluster's CPU to make sure the CPU (and cluster) power is > ON while coresight component of the cluster is being accessed (using smp_call_function_single()). > > The use of power-domains in (1) will limit this to PSCI OS-Initiated mode, > to have this support on PSCI Platform-Coordinated mode too, probably instead of power-domains, > cpu-maps (which also defines the clusters) from device tree is a better choice which will give > the information on which CPU belongs to which cluster. > > (2) ensured that scheduling happened on intended CPU and while the access is in progress, CPU (and > cluster) will not enter power down in between. > >> >>> It doesn’t really send IPI to wakeup CPU device (It don’t have >>> .power_on/.power_off) callback implemented which gets invoked from >>> .runtime_resume callback. This behavior is aligned with the upstream Kernel. >>> >> >> I am quite lost here. Why is it necessary to wake up the CPU? If I understand >> correctly, all of this complexity is meant to ensure that the cluster power >> domain is enabled before any of the funnel registers are accessed. Is that >> correct? > > Yes, This is to ensure that CPU (and cluster) power is ON while coresight components > for same cluster are being accessed. > >> >> If so, and if the cluster domains are already defined as the power domains for >> these funnel devices, then they should be requested to power on automatically >> before any register access occurs. Is that not the case? > > Cluster power-domains will be only available for PSCI OS-initiated mode but also > will not help for cases where all CPUs in cluster are hotplugged off as hotplugs are > platform coordinated. > > After discussion with our HW team to automatically request power on for coresight > component GPR [1] can be used but they seems not working as intended on the existing > SoCs and will be available on next generation SoC. > > [1] https://developer.arm.com/documentation/ddi0480/d/Functional-Overview/Granular-Power-Requestor > >> >> What am I missing in this reasoning? >> >> The only explanation I can see is that the firmware does not properly honor >> power-domain requests coming directly from the OS. I believe that may be the >> case, but I would be glad to be proven wrong. >> > > please see below comment for more details, This seems not a firmware issue. > >>>> >>>>> Unlike system-level CoreSight devices, these components share the CPU cluster's >>>>> power domain. When the cluster enters low-power mode (LPM), their registers >>>>> become inaccessible. Notably, `pm_runtime_get` alone cannot bring the cluster >>>>> out of LPM, making standard register access unreliable. >>>>> >>>> >>>> Are these devices the only ones on the system that are uniquely bound to >>>> cluster-level power domains? If not, what additional devices share this >>>> dependency so that we can understand how they are managed in comparison? >>>> >>> >>> Yes, devices like ETM and TRBE also share this power domain and access constraint. >>> Their drivers naturally handle enablement/disablement on the specific CPU they >>> belong to (e.g., via hotplug callbacks or existing smp_call_function paths). >> >> I understand many things are possible to implement, but the key question >> remains: why doesn’t the existing OSI mechanism - added specifically to cover >> cases like this solve the problem today? >> >> Especially on platforms with OSI enabled, what concrete limitation forces us >> into this additional “wake-up” path instead of relying on OSI to manage the >> dependency/power sequencing? > > + Ulf in loop. > > Current platforms with OSI enabled, Linux PSCI do not implement the power_on/power_off > requests, as far as i know, runtime PM was never meant to implement this part and > pm_runtime_get_sync() (from drivers/cpuidle/cpuidle-psci.c) call is only used to convey > to cluster power domains about a child CPU/ sub domain being on after it has already > been landed in Linux. > > The standalone invoke of pm_runtime_get_sync() from another CPU do not really turn on/get > the CPU (and cluster), as the CPUs either use CPUidle / CPU hotplug paths to enter/exit > low power mode. > > To put it other way, > For a hot-plugged off CPU, invoking a pm_runtime_get_sync() won't get the CPU (and make > its cluster power domain) ON. In order to turn on the CPU, one has to still request > the online of the CPU, say via sysfs command echo 1 > /sys/devices/system/cpu/cpuX/online > which would invoke PSCI CPU_ON function and the power domain for CPU gets marked as ON > only after CPU already landed in Linux via psci_idle_cpuhp_up() invoking pm_runtime_get_sync(). > > I used specific hotplug example but same applies to idle powered down CPU (or Cluster) too. > >> >>>>> To address this, the series introduces: >>>>> - Identifying cluster-bound devices via a new `qcom,cpu-bound-components` >>>>> device tree property. >>>> >>>> Really, no please. >>>> >>> >>> Our objective is to determine which CoreSight components are physically locate >>> within the CPU cluster power domain. >>> >>> Would it be acceptable to derive this relationship from the existing >>> power-domains binding? >> >> In my opinion, this is not merely a possibility but an explicit expectation. >> >>> For example, if a Funnel or Replicator node is linked to a power-domains >>> entry that specifies a cpumask, the driver could recognize this shared >>> dependency and automatically apply the appropriate cluster-aware behavior. >>> >> >> Sure, but for the driver to use that information, we need clear explanation >> for all the questions above. In short, why it is not working with the existing >> PSCI domain idle support. >> > > Explained above. > > Thanks, > Maulik