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Fri, 14 Aug 2026 03:25:02 -0700 (PDT) X-Received: by 2002:a05:6a20:6f04:b0:3bf:6e72:68f9 with SMTP id adf61e73a8af0-3cc720e1af9mr5407807637.38.1786703101528; Fri, 14 Aug 2026 03:25:01 -0700 (PDT) Received: from [10.206.101.140] ([202.46.23.25]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-320d61e1568sm3161720eec.11.2026.08.14.03.24.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Aug 2026 03:25:01 -0700 (PDT) Message-ID: Date: Fri, 14 Aug 2026 15:54:52 +0530 Precedence: bulk X-Mailing-List: linux-kernel@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> <26a880b2-5f37-43be-ae8b-2c0c27c777a1@kernel.org> From: Vishnu Reddy In-Reply-To: <26a880b2-5f37-43be-ae8b-2c0c27c777a1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-GUID: qnDPX-xfQsQ55vEfzYwgqXEMztMDqiX_ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE0MDA3OCBTYWx0ZWRfXxAjnGObDCb3F uLH/GPpReZy56oTCPu8QFsP+RqsqmMHZlWuV186ou+bAEYKxdXsCDSjGPjP3vz0YWTXbwobLb8t 93XchupTLL8xDRoIo6EMOHB5e/jgv5tul8pW1fN0UKG8QckQhhQU3eI8fqnP+R024i2GfxvFHLX XgXh+sNeCc2Kd3j+1rs4TMvG167ZVE9+LNWmoCQnKgT2VrYGy21eMNcapwfDeswI0LG496vaTf2 4ER3EWW3FQ9IwfsBbXSzFN2v6vEhzTDRVy7r8jE7Q9kY4jyhsmGl602O2BRz0a3fLu3R3+1EGau 8LsMpWpF3J6zuGiIHCt0UVubRqYnXzK8IwD58Qo4BwrWVw9WByGXnpOAUvrpkY5II6eKLMR801r 4oF/h5FXdgjHVDYsKn92k/aHGJfGpsOKrPXCoQ5gProuO1ye2qp9n63bqk+cfDrcnh+Fd2WiGPG pP9I9y/GvythqP9SiCg== X-Authority-Analysis: v=2.4 cv=UrdT8ewB c=1 sm=1 tr=0 ts=6a7eecff cx=c_pps a=Oh5Dbbf/trHjhBongsHeRQ==:117 a=ZePRamnt/+rB5gQjfz0u9A==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=mqT1Idva8bgf30cmp0IA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=_Vgx9l1VpLgwpw_dHYaR:22 X-Proofpoint-ORIG-GUID: qnDPX-xfQsQ55vEfzYwgqXEMztMDqiX_ X-Proofpoint-Spam-Info: AW1haW4tMjYwODE0MDA3OCBTYWx0ZWRfXwedZRK+O8GK0 IwEoNJ4R5lhvXyw8y8A1kHgnBcX+7h8YJrW89o72SD6yFgIkY2st7HuSUkDLPivNGyJMIzgjSZ7 ccfPt9EQFxErVrEz6HL78JqUzLDlXCY= 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 priorityscore=1501 impostorscore=0 clxscore=1015 lowpriorityscore=0 phishscore=0 spamscore=0 suspectscore=0 adultscore=0 malwarescore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608140078 On 8/14/2026 3:26 PM, Krzysztof Kozlowski wrote: > On 14/08/2026 11:49, Vishnu Reddy wrote: >> 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. > Again, no... or explain why. Missing dma-coherent is not a fix, but > rather optimisation, but you claimed it is a fix. Explain why. Is the dma-coherent flag only for skipping cache sync? I might be repeating here — it enables the hardware level snoop between CPU caches and DMA memory. Without dma-coherent, the CPU cache and the memory which VPU accesses aren't in sync at the hardware level, which is what caused the corruption. So dma-coherent is the proper fix here, and that's why I've mentioned it as a fix. Do you have any opinion on how you'd prefer to handle this? Please share. > Best regards, > Krzysztof >