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[199.106.103.254]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2bdd1cf0115sm357385eec.8.2026.02.25.15.18.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Feb 2026 15:18:30 -0800 (PST) Message-ID: <3f06453a-ac7e-46e0-8d37-e0f9980b438d@oss.qualcomm.com> Date: Wed, 25 Feb 2026 15:18:29 -0800 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 01/18] accel/qda: Add Qualcomm QDA DSP accelerator driver docs To: Dmitry Baryshkov Cc: Bjorn Andersson , Ekansh Gupta , 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-v1-1-fe46a9c1a046@oss.qualcomm.com> <5a278b02-f2ad-408b-b0ad-f2297817bd7e@oss.qualcomm.com> <4e4b50fe-1091-451e-b854-f7b061ebd88d@oss.qualcomm.com> Content-Language: en-US From: Trilok Soni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-ORIG-GUID: 5-5U8fVGKJkYGHtHye2txoty5_5k0swR X-Authority-Analysis: v=2.4 cv=IqMTsb/g c=1 sm=1 tr=0 ts=699f8348 cx=c_pps a=cFYjgdjTJScbgFmBucgdfQ==:117 a=JYp8KDb2vCoCEuGobkYCKw==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=_glEPmIy2e8OvE2BGh3C:22 a=AmUwcyaVtIZmdcZSVHAA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=scEy_gLbYbu1JhEsrz4S:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI1MDIyMiBTYWx0ZWRfXxTdr0LvCn85G XF9ynwj9JW/JkjzICTYpZVP1JqAtvlyX6iaZf+NreeMt6HCsmaT/7t+uhBEYvYypAq4X4+Is67p FM0K4nZlCtNCIwudscD2qYFEwvvqNeQH+bsxcb0QJ+luxmmfugw+A7/yb7lGwEbG+WntLvW0Ap8 lAFddaPl2I6xHf94uCSOKOE/zL7wWxP4Mg8XWy7YodAb4fzIskxCiYZH7OjYYnit6ainMSKIC53 HTR7wSW8aQI5mNuM4gngKv04pzGtw8uP/eVjxmpKYlzXZawcZthEfsmq7F/wHr9CF16F0JGK1E7 zRtk09cGW/uDV1F9LHoqzziO50m+H/blpJ9bT8tJ2MfuGgOvMN2oOHgWZl0jM+SSolxpnKoMJPd QAcR9zZFwKl/c1n45oEXjr7Y2p9nt3j7Hmxs0gtF2DS0afQEzw3mLvD9NGFW/y8LCt/FeWdRKOn adPa3JXm9DwyJpryJsQ== X-Proofpoint-GUID: 5-5U8fVGKJkYGHtHye2txoty5_5k0swR 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_04,2026-02-25_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 adultscore=0 impostorscore=0 spamscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2602250222 On 2/25/2026 11:40 AM, Dmitry Baryshkov wrote: > On Wed, Feb 25, 2026 at 11:16:26AM -0800, Trilok Soni wrote: >> On 2/25/2026 7:12 AM, Bjorn Andersson wrote: >>> On Wed, Feb 25, 2026 at 07:47:08PM +0530, Ekansh Gupta wrote: >>>> >>>> >>>> On 2/24/2026 9:03 AM, Trilok Soni wrote: >>>>> On 2/23/2026 11:08 AM, Ekansh Gupta wrote: >>>>>> Add initial documentation for the Qualcomm DSP Accelerator (QDA) driver >>>>>> integrated in the DRM accel subsystem. >>>>>> >>>>>> The new docs introduce QDA as a DRM/accel-based implementation of >>>>>> Hexagon DSP offload that is intended as a modern alternative to the >>>>>> legacy FastRPC driver in drivers/misc. The text describes the driver >>>>>> motivation, high-level architecture and interaction with IOMMU context >>>>>> banks, GEM-based buffer management and the RPMsg transport. >>>>>> >>>>>> The user-space facing section documents the main QDA IOCTLs used to >>>>>> establish DSP sessions, manage GEM buffer objects and invoke remote >>>>>> procedures using the FastRPC protocol, along with a typical lifecycle >>>>>> example for applications. >>>>>> >>>>>> Finally, the driver is wired into the Compute Accelerators >>>>>> documentation index under Documentation/accel, and a brief debugging >>>>>> section shows how to enable dynamic debug for the QDA implementation. >>>>> So existing applications written over character device UAPI needs to be >>>>> rewritten over new UAPI and it will be broken once this driver gets >>>>> merged? Are we going to keep both the drivers in the Linux kernel >>>>> and not deprecate the /char device one? >>>>> >>>>> Is Qualcomm going to provide the wrapper library in the userspace >>>>> so that existing applications by our customers and developers >>>>> keep working w/ the newer kernel if the char interface based >>>>> driver gets deprecated? It is not clear from your text above. >>>> Thanks for raising this, Trilok. >>>> >>>> This is one of the open items that I have. I'm not exactly sure what would be the >>>> acceptable way for this.  >>>> >>>> As you mentioned, applications that rely on /dev/fastrpc* might not work on QDA >>>> without modification. >>>> >>>> I was thinking in the same lines as you have mentioned and  having some shim/compat >>>> driver to translate FastRPC UAPI to QDA. The compat driver would expose the existing >>>> character devices and route the calls to QDA. The compat driver could be built via Kconfig. >>>> >>> >>> This is a fundamental requirement, you need to address this in order for >>> this to move forward. >>> >>> Which makes me wonder if it would be possible to reach an accel driver >>> through incremental transition of the current driver, instead of just >>> dropping in a few thousand lines of new code/design. >>> >>>> However, I haven’t encountered an example of such a UAPI‑translation driver in the kernel >>>> before, so I would want guidance from maintainers on whether this is an acceptable >>>> model or not. >>>> >>>> Regarding your question about library, all the APIs exposed by github/fastrpc library are kept >>>> unchanged in terms of definitions and expectation. The same project can be build for both >>>> FastRPC and QDA based on configure options. So, the applications using github/fastrpc should >>>> not face any problem if the libs is built with proper configure options. >>>> >>> >>> You're assuming that the kernel and userspace are a unified piece of >>> software, they are not. It must be possible for me to install a new >>> kernel package without having to replace the userspace libraries. >> >> Thank you Bjorn for providing the inputs. >> >> I also foresee that we will be stop adding (or already happened) new features >> into the existing fastrpc driver, so calling the new driver as an alternative >> is in oversold category. >> >> You are pretty much began the deprecating the existing fastrpc driver, so let's >> just mention it if that is the case and provide migration/shim path so that >> existing binaries doesn't break. > > I agree that we need a migration path, but I'd really focus on it after > getting at least basic parts of the QDA reviewed and agreed upon. > Otherwise the shim layer will be reworked again and again with no > immediate added benefit. > I am fine with the review to be continued, this is RFC series anyway. We should also decide the design of the shim layer here as well. I prefer to not have multiple RFC revisions here if we don't agree on the basic requirements which leads to acceptance of this new driver. ---Trilok Soni