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Fri, 24 Apr 2026 05:42:25 -0700 (PDT) X-Received: by 2002:a17:90a:da8f:b0:35e:594a:5b75 with SMTP id 98e67ed59e1d1-361404c1034mr32348850a91.25.1777034544617; Fri, 24 Apr 2026 05:42:24 -0700 (PDT) Received: from [10.239.60.18] ([106.192.26.241]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-361410b998fsm23315385a91.13.2026.04.24.05.42.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Apr 2026 05:42:24 -0700 (PDT) Message-ID: <1e039dd5-da3f-19b2-ef98-29e64fdd925d@oss.qualcomm.com> Date: Fri, 24 Apr 2026 18:12:09 +0530 Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev 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 v2 02/13] drivers: base: Add generic dma context bus Content-Language: en-US To: Greg Kroah-Hartman Cc: Bryan O'Donoghue , Vikash Garodia , Dikshita Agarwal , Abhinav Kumar , Mauro Carvalho Chehab , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Joerg Roedel , Will Deacon , Robin Murphy , Bjorn Andersson , Konrad Dybcio , Stefan Schmidt , Hans Verkuil , "Rafael J. Wysocki" , Danilo Krummrich , Thierry Reding , Mikko Perttunen , David Airlie , Simona Vetter , Jonathan Hunter , linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, driver-core@lists.linux.dev, dri-devel@lists.freedesktop.org, linux-tegra@vger.kernel.org, Ekansh Gupta , Dmitry Baryshkov References: <20260423-glymur-v2-0-0296bccb9f4e@oss.qualcomm.com> <20260423-glymur-v2-2-0296bccb9f4e@oss.qualcomm.com> <2026042346-trustable-register-095a@gregkh> <06c04947-e72e-679b-493b-e112d693f391@oss.qualcomm.com> <2026042422-deem-chemist-8d0f@gregkh> <4c3fa710-f61a-4aad-622d-54909190cb9e@oss.qualcomm.com> <2026042428-blemish-helpline-7d8d@gregkh> From: Vishnu Reddy In-Reply-To: <2026042428-blemish-helpline-7d8d@gregkh> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: Ltnovb0RuCOA6P-S-Dglvqtd23PZ8Sxg X-Authority-Analysis: v=2.4 cv=VOjtWdPX c=1 sm=1 tr=0 ts=69eb6532 cx=c_pps a=vVfyC5vLCtgYJKYeQD43oA==:117 a=K3jt3zD9TrcZs+Uyli2v9A==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=_K5XuSEh1TEqbUxoQ0s3:22 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=EUspDBNiAAAA:8 a=fZobZ8Dl1N5RqnsFfjAA:9 a=QEXdDO2ut3YA:10 a=rl5im9kqc5Lf4LNbBjHf:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-ORIG-GUID: Ltnovb0RuCOA6P-S-Dglvqtd23PZ8Sxg X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDI0MDExNyBTYWx0ZWRfX+1utjQ1h0HuP UbVjoEmK6qt+1tYy61uRENtb7OKF5cvUFTP76dat6n9YhDc+HTKcs6lv+gOPmFkEmmbkZBdx42b tmsiWiBoP8KzHVjEFtlkrb90jzd/24/W2LwgVIn9puFrr2KPEGtYw5DkczJ3jKUTGTR4FUNLDma sBPF3+PWnnpfDSGZF21LEbu+6AndWUwixl/6c8nk4JibiGCJ/lPMn2qEpe3snMl7kR3X+LMH22c qGEzrVGHMi+kEu4dmhwNr17jfk0rRzBEYwlkMhRQ2GFHFqMiDGzf9hqY+HyXOWjW9O3PcQ7/zQB vsEGqzNatl52tKS8WDJC4cn3KdznSLoIHrMWAojyxvst6PjK0QAzlxZJZ4eQCb0qFeH6R1ltMjZ n0vqdMUvBZjsdbP+wDFO180cRiFoNOGye7Mne48hXuzeiXIbM4xGI0Br+/BY9dqa76ELTuNWDH+ 8fyPfAkWj4qGJPoPxMw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-23_03,2026-04-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 lowpriorityscore=0 impostorscore=0 spamscore=0 priorityscore=1501 bulkscore=0 suspectscore=0 malwarescore=0 clxscore=1015 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2604240117 On 4/24/2026 5:25 PM, Greg Kroah-Hartman wrote: > On Fri, Apr 24, 2026 at 05:15:02PM +0530, Vishnu Reddy wrote: >> On 4/24/2026 4:43 PM, Greg Kroah-Hartman wrote: >>> On Fri, Apr 24, 2026 at 04:01:13PM +0530, Vishnu Reddy wrote: >>>> On 4/23/2026 7:07 PM, Greg Kroah-Hartman wrote: >>>>> On Thu, Apr 23, 2026 at 06:59:31PM +0530, Vishnu Reddy wrote: >>>>>> From: Ekansh Gupta >>>>>> >>>>>> When a driver needs to create virtual device at runtime and map it to >>>>>> an IOMMU context for memory isolation, there is no common bus available >>>>>> for this purpose. Each driver ends up implementing its own bus type, >>>>>> leading to duplicated logic across multiple drivers. >>>>>> >>>>>> host1x driver implemented its own bus type to attach an IOMMU context to >>>>>> a dynamically created device. The Iris VPU driver now has the same >>>>>> requirement. Rather than duplicating the same bus logic again, a shared >>>>>> bus type is introduced under drivers/base that multiple drivers can use >>>>>> directly. >>>>>> >>>>>> The bus takes care of creating a device and attaching the IOMMU context >>>>>> to it based on the client inputs. >>>>>> >>>>>> Suggested-by: Dmitry Baryshkov >>>>>> Signed-off-by: Ekansh Gupta >>>>>> Signed-off-by: Vikash Garodia >>>>>> Signed-off-by: Vishnu Reddy >>>>>> --- >>>>>> drivers/base/Kconfig | 3 ++ >>>>>> drivers/base/Makefile | 1 + >>>>>> drivers/base/dma_context_bus.c | 77 +++++++++++++++++++++++++++++++++++++++++ >>>>>> include/linux/dma_context_bus.h | 26 ++++++++++++++ >>>>>> 4 files changed, 107 insertions(+) >>>>> as you can not have a device on multiple busses at the same time, this >>>>> makes no sense to me at all. "dma context" is a bus-specific thing, so >>>>> please add it to the bus that you are wanting it for. It can't be a >>>>> generic bus as that just doesn't work. >>>>> >>>>> Or what am I missing here? >>>>> >>>>> And why is DMA somehow "special" here from any other hardware attribute? >>>> Let me give brief information which was discussed, in the initial series, >>>> the iris VPU used platform bus for dynamically created devices and we got >>>> the comment/suggestion from Robin to implement a proper bus_type with a >>>> .dma_configure callback. >>>> >>>> https://lore.kernel.org/all/02b3d0f5-f94c-43cd-93af-97cfcf7751b1@arm.com/ >>>> >>>> based on the discussion, implemented the dma_context_bus and used for iris >>>> VPU devices instead of platform bus. >>> Why not make a irus_vpu_bus where you can do what you want? >> Initially iris_vpu_bus was introduced, and it was made generic based on the >> discussion, >> >> https://lore.kernel.org/all/20260227-kaanapali-iris-v2-3-850043ac3933@oss.qualcomm.com/ > I don't really see that request here, I see a "make this better and more > generic for other busses" but that does not mean "dump it into > drivers/bus/ for someone else to maintain" :) > >>>> Here, the device have only one bus (dma_context_bus), not multiple buses. >>>> >>>> Regarding the "DMA" naming, the core operation of this bus is its >>>> .dma_configure callback, which calls of_dma_configure_id() to map the device >>>> to a corresponding IOMMU stream ID. The name "dma_context" reflects this >>>> purpose. >>>> >>>> I am open to suggestions from you or Robin or anyone else, if there is a >>>> better or preferred way to achieve this, I am happy to consider it and >>>> rework the implementation accordingly. >>> As there is only one user, just make this your own bus please and do all >>> of the needed bus operations for your devices there (i.e. don't hang an >>> "empty" device off of it.) >> The reasoning behind to make it generic was to have more users - host1x, >> Iris VPU, QDA on the generic context bus, instead of each of them having >> their own. Let me know if you suggest to have the iris_vpu_bus. > But you did not add such users here, so how would we know this? > > And still, I have no idea what this bus really is doing. Is it dynamic? > Is it self-describing? Why not just use aux-bus? What is it supposed > to be doing and used for? This bus will allow users to create a dynamic device and map to IOMMU stream ID via .dma_configure callback which calls the of_dma_confgure_id() based on the user inputs. This bus is under the iommu_buses list to register for bus notifier callbacks for iommu_probe_device() and iommu_release_device() during add and remove. auxilary bus don't have the .dma_callback and bus notifier callbacks where it can do iommu_probe_device() and iommu_release_device(). iommu_release_device(), being a static api, need to be called from bus notifier callbacks which should be under the list of iommu_buses. > > still totally confused, > > greg k-h