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Thu, 13 Aug 2026 22:29:42 -0700 (PDT) X-Received: by 2002:a05:6a20:12d2:b0:3c3:9746:1fcb with SMTP id adf61e73a8af0-3cc71dc524bmr3468828637.35.1786685382278; Thu, 13 Aug 2026 22:29:42 -0700 (PDT) Received: from [10.206.101.140] ([202.46.23.25]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-320d61e1568sm56924eec.11.2026.08.13.22.29.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Aug 2026 22:29:41 -0700 (PDT) Message-ID: <4b34e718-0878-25cc-a5bd-0d8858df5133@oss.qualcomm.com> Date: Fri, 14 Aug 2026 10:59:32 +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> From: Vishnu Reddy In-Reply-To: <20260813-frisky-augmented-crow-fd5d3d@quoll> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Authority-Analysis: v=2.4 cv=NsfhtcdJ c=1 sm=1 tr=0 ts=6a7ea7c7 cx=c_pps a=rz3CxIlbcmazkYymdCej/Q==:117 a=ZePRamnt/+rB5gQjfz0u9A==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=ZpdpYltYx_vBUK5n70dp:22 a=2wY4_1yd3szzHPvr_iMA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=bFCP_H2QrGi7Okbo017w:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE0MDA0MCBTYWx0ZWRfXyKP2VmHAXSE/ LfVwfq6quHB4AVeoNt8EMcObpVhjdYCNQiBtS34fLzdmtc/uoz25u/7hA/XfI8E7wwkyBwyR1qL IY3banjDF/al54nNocovj0fA5B3+3UZaomyRmBSAldtxHKbYv8meUVBZYV7rLJL5fwicHqnOW2e QL/EQuEn8m3ExQjPrwuIhsByHKIkOVhX+YTMaEETakfhrGTinMI58Xd53jBDvqgXLSanQM43TVR csa2xhiIZgny7jiouBS+TWGb+hKH6jU8XioQpov6IhjTHU/evnhZJ6O8dJXb83QAOneKGmlsmry enOQYTlhTOyDvR2CJUjg5KYE4gbOdXQ13Ckjfkb9sJRG0oPSlQSSHE1zsBizpKPkhjOmUREFoFO MetNMXY8t9RPY1+jUhCBqLPkL2mLF4HzrC8AvMba+lCJ304Sj7I8ZjumRBn6JUMi1RNOZzYr4TH mh2YELf0OaqzF4b8L/w== X-Proofpoint-ORIG-GUID: xNiaDk81nrPxs3PQJJ0GI39YY9K0N9qr X-Proofpoint-GUID: xNiaDk81nrPxs3PQJJ0GI39YY9K0N9qr X-Proofpoint-Spam-Info: AW1haW4tMjYwODE0MDA0MCBTYWx0ZWRfX0PJW5XO7hNBZ 8rcWteTHbezycjvoBTYJS7ruZtbwnUkd7/RDH20GFTRoJJWv2f9CUtxd1r9K3X0HZIjlW02c4E6 GferwlTU6EgJb3TBdkJk+64STr4Qa8I= 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_02,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 lowpriorityscore=0 spamscore=0 bulkscore=0 adultscore=0 clxscore=1015 priorityscore=1501 malwarescore=0 suspectscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608140040 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. 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. > Best regards, > Krzysztof > >