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Fri, 14 Aug 2026 02:50:00 -0700 (PDT) X-Received: by 2002:a05:6a20:9f93:b0:3bd:3800:7538 with SMTP id adf61e73a8af0-3cc71de3f87mr4852449637.33.1786700999644; Fri, 14 Aug 2026 02:49:59 -0700 (PDT) Received: from [10.206.101.140] ([202.46.23.25]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-320d5bd9fd3sm2621667eec.4.2026.08.14.02.49.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Aug 2026 02:49:59 -0700 (PDT) Message-ID: Date: Fri, 14 Aug 2026 15:19:51 +0530 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH 2/4] arm64: dts: qcom: sc7280: Add dma-coherent property into venus node Content-Language: en-US To: Krzysztof Kozlowski Cc: Bryan O'Donoghue , Vikash Garodia , Dikshita Agarwal , Mauro Carvalho Chehab , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Stanimir Varbanov , Mansur Alisha Shaik , Bjorn Andersson , Konrad Dybcio , Abhinav Kumar , Hans Verkuil , Stefan Schmidt , Hans Verkuil , linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260801-iris-fixes-dma-pseq-fint-v1-0-aba0cb22f6ab@oss.qualcomm.com> <20260801-iris-fixes-dma-pseq-fint-v1-2-aba0cb22f6ab@oss.qualcomm.com> <20260813-frisky-augmented-crow-fd5d3d@quoll> <4b34e718-0878-25cc-a5bd-0d8858df5133@oss.qualcomm.com> <30195e14-0dcb-476d-af0d-f85ee57e2aa5@kernel.org> From: Vishnu Reddy In-Reply-To: <30195e14-0dcb-476d-af0d-f85ee57e2aa5@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE0MDA3NCBTYWx0ZWRfXzCenuN/fzXb5 8smLgYTG6Sicmam67L/dXfs02n9Qd8ZGsm/rPzKpGL8EuIZ33ACDgq8qT+YUnEnYazOxzRZ2DLz 5W78Czu/JGBFfz6+AWpQWzGWsluguct0zICBTwHhyN9rIQsqDI/OOCyIYTaWv0RR2x6WipasqHN Xk/+8xAajCk3FEw1yyQaoWK0gUE9w1gIge3VgUlfKqvLULHp8SfcHxtecI8FtMhF9x4NJ779y2c V77Lwdr6PLEwbSAXAPqTaK5ZQhUw+4QbiO/yjQBHJCe8G3jR5NV8bnOnmwEQI1bukESC95baCGY jCP38pYjJXNNoPG7fVj7+QdHI0WUCIswZukAb/MEuuG4BknqYKxyhOOMcYJMvb+31eTpGITc3zI VOlyzBWiuplc4FQ5XUWANmWMFCIBSOeCK/0lDEIl66u7EzETAxgJS4i7UTZy0uO9UDG9LvqXOP+ ZHfMHlSrIkr2BOdY8Kw== X-Authority-Analysis: v=2.4 cv=DdMnbPtW c=1 sm=1 tr=0 ts=6a7ee4c8 cx=c_pps a=oF/VQ+ItUULfLr/lQ2/icg==:117 a=ZePRamnt/+rB5gQjfz0u9A==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=gowsoOTTUOVcmtlkKump:22 a=V9F15ByMrN-4acUeBR0A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=3WC7DwWrALyhR5TkjVHa:22 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE0MDA3NCBTYWx0ZWRfX7VRTQqyhfXee p/C0SbsID8agzQGayfe2BGeO/4ds9BbTq9ZpCgCUL/9oI0AT3qeVzFMzxBDgV4lHdXOB7meld/N 6hfSbCtBpPKHXVkdN9xZm6P3LlVqyn4= X-Proofpoint-GUID: Z-sPHZ3F6Zc0jFYrbKFtetK-kqHwWvL7 X-Proofpoint-ORIG-GUID: Z-sPHZ3F6Zc0jFYrbKFtetK-kqHwWvL7 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-14_03,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 phishscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 spamscore=0 bulkscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608140074 On 8/14/2026 12:01 PM, Krzysztof Kozlowski wrote: > On 14/08/2026 07:29, Vishnu Reddy wrote: >> On 8/13/2026 2:49 PM, Krzysztof Kozlowski wrote: >>> On Sat, Aug 01, 2026 at 01:07:28PM +0530, Vishnu Reddy wrote: >>>> While testing with some higher resolution clips, the venus hardware >>>> triggers a fault due to wrong input data being received. Corruption >>>> was also observed in the captured output when the client dumped it >>>> to a file. >>>> >>>> On debugging, this was traced to the venus node not declaring >>>> dma-coherent. As a result, DMA buffers shared between the CPU and the >>>> venus video hardware/controller are not guaranteed to be I/O coherent: >>>> CPU writes to an input buffer can remain in CPU caches without being >>>> visible to the video hardware when it reads the same buffer, so the >>>> hardware receives input data that does not match what the CPU wrote. >>>> Likewise, on the capture path, data written by the video hardware to >>>> the output buffer may not be visible to the CPU, so the client reads >>>> stale or partial data, resulting in corruption. >>>> >>>> Add the dma-coherent property to the venus node so that DMA buffers >>>> shared between the CPU and the video hardware and controller remain >>>> coherent. >>>> >>>> Fixes: 37613aee2179 ("arm64: dts: qcom: sc7280: Add venus DT node") >>> Really does not look like a fix. How skipping a cache sync can fix >>> anything exactly? >> dma-coherent tells the kernel that this device DMA path is hardware-coherent, >> so the SMMU maps its buffers as cacheable. That attribute is what causes the >> coherent interconnect to snoop CPU cache lines on every VPU transaction, so >> hardware keeps CPU caches and VPU-visible memory in sync — which is why the >> dma-coherent property lets us skip the unnecessary cache clean/invalidate. > You just repeated what I wrote. What for? > >> If a device doesn't support I/O coherence, its buffers would instead be mapped >> non-cacheable, no snooping would occur, and the driver would need explicit >> dma_sync_*() calls at each transition. Venus on SC7280 does support I/O >> coherence, so dma-coherent describes that existing hardware capability to >> the DMA subsystem. > How does this anyhow explain your commit msg? Are you saying driver is > buggy that it misses sync calls? No, driver is not buggy here. dma-coherent flag is missed in the dt node. > Best regards, > Krzysztof >