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[129.46.96.20]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-375212e9e03sm23040256eec.23.2026.11.10.19.30.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 19:30:01 -0800 (PST) Date: Tue, 10 Nov 2026 19:29:59 -0800 From: Peter Chen To: Akash Kumar Cc: Greg Kroah-Hartman , Bjorn Andersson , Konrad Dybcio , Rob Herring , Dmitry Baryshkov , Krzysztof Kozlowski , Conor Dooley , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org Subject: Re: [PATCH v2] usb: dwc3: Update nominal max votes for qcom usb Message-ID: References: <20261105100626.2003771-1-akash.kumar@oss.qualcomm.com> X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTExMDAxMyBTYWx0ZWRfX1spy6oV0nU7w PspqwXpMHqjyJf91aIVeGO07PWNIbMoXtATeByQW+kW6H26f3pP33aN91ISsSp4K6NYy6uzZ0yL W2KEPs3aE2G7mYSdlhuiKRkmSgP2KO+NrePnXHcAJip9oWCPf4tN2WIcRh4JVjgg4QUnG6WynKm z4QEsLH76bymQOAMsLJ8ptZAqhTJk/qx2lnn8GasysnP/Pf/7/tYtdypI+RsJsVgGYeuSrOTf2L EI8H7QDGovOYwg40ESdsDnvb0xlOG6+isr7p0yqMY2/Au3jUU6i9GRRw6LKKuSG66hlWrOMwjhQ JUF8TOY0LCOvVS1GgKKpP+pkgBEAL8RFgP1Mn7V4XsoeC/QY/Nq6jKEer/jGh0YAPxE8FU1OB53 SAeowHjt8ep61IzOC6JrTEEkAoZwTpwUtiETNqG15P6rbowpzcqVgKFu0dpJnNJV2fjO8pLl9je 4WgBE2vK5RI4I+J+S3Q== X-Authority-Analysis: v=2.4 cv=Ee1d0/mC c=1 sm=1 tr=0 ts=6af3e13c cx=c_pps a=Uww141gWH0fZj/3QKPojxA==:117 a=ouPCqIW2jiPt+lZRy3xVPw==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=YMgV9FUhrdKAYTUUvYB2:22 a=kQgC6_mu_KQiaI9rv0QA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=PxkB5W3o20Ba91AHUih5:22 X-Proofpoint-Spam-Info: AW1haW4tMjYxMTExMDAxMyBTYWx0ZWRfXypFYTJBbGBFP KvxuqO/AWAJ2P0w+jIxt0KZK1julfzrUscUq0GcfDEgRTSuARDmGArUeRHCGI4Y4nOwtxKynl0t YE6WzbEIRki9aTZ18l00SrNjrptn76I= X-Proofpoint-GUID: SrxlJX7DG02JbXGbw-Z1gXR10bSxOAvj X-Proofpoint-ORIG-GUID: SrxlJX7DG02JbXGbw-Z1gXR10bSxOAvj X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-11_01,2026-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 suspectscore=0 clxscore=1015 adultscore=0 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611110013 On 26-11-10 18:11:31, Akash Kumar wrote: > > On 09-11-2026 14:30, Peter Chen wrote: > > On 26-11-05 15:32:16, Akash Kumar wrote: > > > Increase the nominal max USB memory bandwidth vote to let DDR scale > > > higher within its nominal corner, fixing glitches seen during > > > simultaneous USB audio use cases. > > > > > > USB_MEMORY_PEAK_SS_BW is raised from 2500 MB/s to 4500 MB/s (+2000 > > > MB/s, ~1.8x). This ICC vote does not by itself determine DDR > > > frequency; the vote-to-frequency mapping is platform-specific and > > > comes from each target's interconnect/OPP table. On the tested > > > targets, the old vote kept DDR pinned at 1 GHz within the nominal > > > corner, even though DDR can run at 1.5 GHz (+50%) within the same > > > corner. At 1 GHz, glitches were observed during multiple concurrent > > > USB audio use cases. > > How we decide which value is suitable, eg, you set 4500 here? > > If DDR can run higher, and we have more stress test case like UAS > > transfer + UVC transfer, do we need this value to be higher? > > > > Is it okay we just set the highest value for USB, there is a platform > > OPP table, and we let ICC choose the highest value for USB at specific > > platform? > > > > Peter > > > Hi Peter, > > 4500 MB/s was arrived at empirically, not computed: we swept the peak SS > vote on each tested target and read back the committed DDR frequency. > 2500 MB/s capped every target at 1 GHz; 4500 MB/s is the smallest common > vote that reliably crosses into the 1.5 GHz nominal step on all of > them without pushing any target into the next corner above nominal. > 1.5 GHz is also the DDR frequency our power team's KPI bandwidth table > accepts as nominal, so this vote keeps us inside the power budget they've > signed off on, not just inside a technically-valid corner. > > We've additionally run isochronous endpoint use cases with this change — > mobile platform passes the full MJPEG test suite at this vote with no regressions. > We've also verified UAC+UVC concurrently: for that combination, > DDR is bumped at runtime on demand by the userspace application > rather than relying on this static floor vote alone. > > That's also why we didn't just vote the platform max and let ICC pick: > not every USB use case needs or should force DDR to its ceiling. > If we voted max unconditionally for all USB activity, DDR would sit > pinned at the highest corner any time a SS device is attached, which shows up > directly as a regression on the power dashboard across every platform using > this shared driver. The static vote here is sized for the common case; > use cases that genuinely need more (like UAC+UVC) bump DDR explicitly at > runtime instead of paying that cost unconditionally. > > In Future, we have a plan to make it configurable from device tree which can > be done based on target. > Akash, thanks for detail explanation. I had not considered power consumption affect. So, we set a default value for balance performance and power at most platforms, in future, we could configure it through device tree or use space according to scenario. -- Thanks, Peter Chen