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Fri, 24 Apr 2026 04:45:15 -0700 (PDT) X-Received: by 2002:a05:6a00:27a8:b0:82f:18fa:1668 with SMTP id d2e1a72fcca58-82f8c91e3cbmr31091150b3a.44.1777031115048; Fri, 24 Apr 2026 04:45:15 -0700 (PDT) Received: from [10.239.60.18] ([106.192.26.241]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82f8ec04448sm27904931b3a.55.2026.04.24.04.45.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Apr 2026 04:45:14 -0700 (PDT) Message-ID: <4c3fa710-f61a-4aad-622d-54909190cb9e@oss.qualcomm.com> Date: Fri, 24 Apr 2026 17:15:02 +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 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> From: Vishnu Reddy In-Reply-To: <2026042422-deem-chemist-8d0f@gregkh> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: KsG5_88ZCRbDkNYA5y1cVFW9RnIo7tz- X-Authority-Analysis: v=2.4 cv=VOjtWdPX c=1 sm=1 tr=0 ts=69eb57cc cx=c_pps a=WW5sKcV1LcKqjgzy2JUPuA==: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=qtrQGJdHBaugJqU6AYUA:9 a=QEXdDO2ut3YA:10 a=OpyuDcXvxspvyRM73sMx:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-ORIG-GUID: KsG5_88ZCRbDkNYA5y1cVFW9RnIo7tz- X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDI0MDExMSBTYWx0ZWRfXxO/t6uOWu3S7 QnEk6ClKKTCKRVrqpn+kfFwsPi5r2CWrQbNx9Agmn+eHRA6iNnVrhpXcSKMSYqSGzhQSIZCSvUR colpMl7YUkHzAfK3F5kD+t2sbTUJteWL4YUURTJKwyOaBe2Bq3jW//aXzFgmxciQNIdifC0DeYu zUe6pxbXQghVgZuOV7Rie47wMUj8SA1Po6RoBDSDS+MF7qcFoyTnUiInp0cGh7uqpUCTrl1r3YH mp4YQ7FrNs2KgGni5+Dc5P+U6VNygudbCQibzoga/9j2ke3yswBySLbMDkIoJj5ka5tRnc8OXSr KmvKNrLzTzyUjDsguAKJosR1DpG4CHqpzRgHRsirBEaNtabhjb3zyevScrSA3Z1ENdgGCI3kjnv NAfDmzqPpK3L4GyRMYgWrhy1iOBsVQnGAJoiayADwUT5+qJOp8wpM4GI//+0ohTvER8WMfmq6FH VsRgqT3/orvQFvIH+gg== 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-2604240111 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/ >> 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. QDA - https://lore.kernel.org/all/20260224-qda-firstpost-v1-4-fe46a9c1a046@oss.qualcomm.com/ Iris VPU - https://lore.kernel.org/all/20260227-kaanapali-iris-v2-3-850043ac3933@oss.qualcomm.com/ > thanks, > > greg k-h