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[2001:14ba:a073:af00:264b:feff:fe8b:be8a]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-389a7a1fcb1sm30525601fa.27.2026.02.25.11.09.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Feb 2026 11:09:55 -0800 (PST) Date: Wed, 25 Feb 2026 21:09:53 +0200 From: Dmitry Baryshkov To: Ekansh Gupta Cc: Oded Gabbay , Jonathan Corbet , Shuah Khan , Joerg Roedel , Will Deacon , Robin Murphy , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Sumit Semwal , Christian =?utf-8?B?S8O2bmln?= , dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, iommu@lists.linux.dev, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, Srinivas Kandagatla , Bharath Kumar , Chenna Kesava Raju Subject: Re: [PATCH RFC 04/18] accel/qda: Add built-in compute CB bus for QDA and integrate with IOMMU Message-ID: References: <20260224-qda-firstpost-v1-0-fe46a9c1a046@oss.qualcomm.com> <20260224-qda-firstpost-v1-4-fe46a9c1a046@oss.qualcomm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI1MDE4MCBTYWx0ZWRfX3NGz1LJhICzJ 3+QpzLdTECsredHML6oen1fBWhLyYOT3neDPIjhzKKdU7CMmVQqWEZxTf1ywpZzfQ3sEGp7S8Wz rkWBNCwQWnEx/oqpbv/4emF2QFMtKgdkXnDZg1PfC/JMfU7OHYd7it5IE02NVvaY60664wK8Upb Tfw6OnzYC3Z8pJrw6SplRjYGWckvgNMz7k3D0xZPpHOCzIS3cTm1LV5yiM3twkl9UDbkP/DP7Sc zKKPZFE8qQYhYeuttWH6vn0dt8HXJGY2YTJz6N1FLk5Xxob4jxbjvIT0Cb94gx27TX9T4LWTryz 4BDnkOkjUEcldmpXoMm6G/4STWVOrvREtBsMpR1orkE7KkQk5h3F1nr74787oJw0O65vLPoEBMj fjAIw3v8qAu02UBUzMBzrEhQK26wtmBoXqSuv5YWtzqyF6Cpnvse/OGEgQSV+n4nS9tT7cbhBQQ kcznYOEJd+ccuh/YG5w== X-Proofpoint-GUID: cdoX_IftJskXgGM3qseMXXvTO_M4KQ1R X-Proofpoint-ORIG-GUID: cdoX_IftJskXgGM3qseMXXvTO_M4KQ1R X-Authority-Analysis: v=2.4 cv=etXSD4pX c=1 sm=1 tr=0 ts=699f4905 cx=c_pps a=HLyN3IcIa5EE8TELMZ618Q==:117 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=HzLeVaNsDn8A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=yBEyVpS31OZj4jLVKcoA:9 a=CjuIK1q_8ugA:10 a=bTQJ7kPSJx9SKPbeHEYW:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-25_02,2026-02-25_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 malwarescore=0 suspectscore=0 bulkscore=0 phishscore=0 spamscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2602250180 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, Feb 25, 2026 at 11:26:52PM +0530, Ekansh Gupta wrote: > > > On 2/24/2026 4:14 AM, Dmitry Baryshkov wrote: > > On Tue, Feb 24, 2026 at 12:38:58AM +0530, Ekansh Gupta wrote: > >> Introduce a built-in compute context-bank (CB) bus used by the Qualcomm > >> DSP accelerator (QDA) driver to represent DSP CB devices that require > >> IOMMU configuration. This separates the CB bus from the QDA driver and > >> allows QDA to remain a loadable module while the bus is always built-in. > > Why? What is the actual problem that you are trying to solve? > Bus needs to be built-in as it is being used by iommu driver. I'll add more details here. It's an implementation detail. Start your commit message with the description of the issue or a problem that you are solving. > > > >> A new bool Kconfig symbol DRM_ACCEL_QDA_COMPUTE_BUS is added and is > > Don't describe the patch contents. Please. > Ack. > > > >> selected by the main DRM_ACCEL_QDA driver. The parent accel Makefile is > >> updated to descend into the QDA directory for both built-in and module > >> builds so that the CB bus is compiled into vmlinux while the driver > >> remains modular. > >> > >> The CB bus is registered at postcore_initcall() time and is exposed to > >> the IOMMU core through iommu_buses[] in the same way as the Tegra > >> host1x context-bus. This enables later patches to create CB devices on > >> this bus and obtain IOMMU domains for them. > > Note, there is nothing QDA-specific in this patch. Please explain, why > > the bus is QDA-specific? Can we generalize it? > I needed a custom bus here to use for the compute cb devices for iommu > configurations, I don't see any reason to keep it QDA-specific. The only requirement > is that this should be enabled built in whenever QDA is enabled. Why? FastRPC uses platform_bus. You need to explain, why it's not correct. > > But if I keep it generic, where should this be placed? Should it be accel(or drm?) specific? drivers/base? Or drivers/iommu? That would totally depend on the issue description. E.g. can we use the same code for host1x? -- With best wishes Dmitry