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Mon, 02 Mar 2026 00:12:38 -0800 (PST) X-Received: by 2002:a05:6a00:414a:b0:81b:8872:ae10 with SMTP id d2e1a72fcca58-8274d8090eemr11013957b3a.0.1772439158150; Mon, 02 Mar 2026 00:12:38 -0800 (PST) Received: from [10.206.99.28] ([202.46.23.25]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8273a060071sm12915292b3a.63.2026.03.02.00.12.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Mar 2026 00:12:37 -0800 (PST) Message-ID: <7c795b4b-3a3f-47fb-9ef9-0b13601f584c@oss.qualcomm.com> Date: Mon, 2 Mar 2026 13:42:30 +0530 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 04/18] accel/qda: Add built-in compute CB bus for QDA and integrate with IOMMU To: Dmitry Baryshkov 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 , =?UTF-8?Q?Christian_K=C3=B6nig?= , 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 References: <20260224-qda-firstpost-v1-0-fe46a9c1a046@oss.qualcomm.com> <20260224-qda-firstpost-v1-4-fe46a9c1a046@oss.qualcomm.com> Content-Language: en-US From: Ekansh Gupta In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAyMDA3MSBTYWx0ZWRfXyVDeBBKa2sN3 72UBadO+ozgOS+pIlcE/XhbHXQUOBJO3jA104PIoQbc3tLRFADi9XuRZ8sAFhBKHc2ZvUbZ75jX /N7c8nvjV7+b1a7UjOibNS4kVSJyhGC0F1LZjKLkViEsgyQrB2X+3RlXHEfWwd9J6jmmt1lKi0+ f8KxSSlm1WWH02N1XbYDlGtyvQbQqsQut7GIwdEIfHI/gHovN0LhUBdBWEjgWySs4Kg8lyCWvHR lfVaGIYcbmTmoU9r5aHkpzp3+t3mOgPWLH4kpcqp0pg0NZFbomO5+J8UgUYGtKS5fgWTn+5r9jf Vgh5tVz68M1S9vcaqnY2+BXZPjGYCnnQkxTvqQhy7SJGjtgr+V47WqgiaLXeQAjx3Hzng5kOHTw ydazTCV8mlkZxLiCge17CtvYhTM5Ww2sm32qR2vRF8nEl2GxAkjWL/Qsw4CEyDYgsYpz74pdEwl xPnNiqqXSzYj0ZC3a9g== X-Authority-Analysis: v=2.4 cv=QfVrf8bv c=1 sm=1 tr=0 ts=69a54677 cx=c_pps a=rEQLjTOiSrHUhVqRoksmgQ==:117 a=ZePRamnt/+rB5gQjfz0u9A==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=jwkSyuDCPDQl0KFoS7wA:9 a=QEXdDO2ut3YA:10 a=2VI0MkxyNR6bbpdq8BZq:22 X-Proofpoint-ORIG-GUID: tbDsSq7lUk6HYzllZyvzDkazPlPEBdLN X-Proofpoint-GUID: tbDsSq7lUk6HYzllZyvzDkazPlPEBdLN 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=2026-03-02_02,2026-02-27_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 priorityscore=1501 spamscore=0 bulkscore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 phishscore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603020071 On 2/26/2026 12:39 AM, Dmitry Baryshkov wrote: > 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. Ack. > >>>> 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. Ack. > >> 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? I'll evaluate and bring this change separately for fastrpc and host1x. > >