From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2545A36F403 for ; Wed, 25 Feb 2026 23:18:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=205.220.180.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772061515; cv=none; b=neJQ+fBFUSAkrbBnTk3gk9VUrxNynOZQmOAD7QG2z7LXFGA9EABTDtkPfaRsus6HkDMDbo6iN6NqzDiJ6SAXnhHMJ7VnTgfy779mw3sViPTjxEQb9t68iyptEsmiItDEeSjLRZgK1qm+3kpZ/Iqp+OCoNH3GQKQ2Ujk0CDyTQNg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772061515; c=relaxed/simple; bh=HhhiVoqh4Q1gSvfSxzm9qMI34m/iQys18sSsZO1HSnE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G8PbE49/qGxyPteUqqGCahH0xEvg+jLU/it9hPzIh4V049VUIJgY8YPZ4TcVv6lJW8S9++E9wS20dCjAvpt5zIr5++wSqPriCKubRHrrW9SNK4ngpaXWU1nA/QmfGsp2p2JWDsWPQop9ZlA4wJ/IWVuDPBM7mf87G3EXTDSBHkA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oss.qualcomm.com; spf=pass smtp.mailfrom=oss.qualcomm.com; dkim=pass (2048-bit key) header.d=qualcomm.com header.i=@qualcomm.com header.b=JpmL+CkW; dkim=pass (2048-bit key) header.d=oss.qualcomm.com header.i=@oss.qualcomm.com header.b=dDPG/FO+; arc=none smtp.client-ip=205.220.180.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oss.qualcomm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oss.qualcomm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=qualcomm.com header.i=@qualcomm.com header.b="JpmL+CkW"; dkim=pass (2048-bit key) header.d=oss.qualcomm.com header.i=@oss.qualcomm.com header.b="dDPG/FO+" Received: from pps.filterd (m0279873.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 61PJ8c3D788487 for ; Wed, 25 Feb 2026 23:18:33 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qualcomm.com; h= cc:content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=qcppdkim1; bh= k1ncu6ArYzJhC1oWtoKaTbf490HS3AonBnLenM3Jd0c=; b=JpmL+CkWYUP0rhkq yvcnpyP/EsHfwQoW0K88N1JAwbxTi+LLkZjH9DnYvIiobtYH5J/g8+9NO85fBMy2 kviXPZxgDBjU9X/GvP4DBmN+EQ3kZmoyKjP7w6eVnJVJzNDhRfpq2IsfE81WQkuh SqGKaB0hOvmonmXYz8t/bTRs9L/qyP0J6vhfIpk7hwpr4X/Oa++bWNC8h1FEQnM0 aRUSD8losKzsY6bDy0GwTFFfO5k1NBw/RQLoC5/2zk+aY+Gn89MIwAMaa4NJeH2v SO1uWYK0vdnDIr369SYLjwZ1kJxo32PT1fieroRk0aGGqmVEoRy2LpCjqL1JCwzX OLvqSw== Received: from mail-dy1-f197.google.com (mail-dy1-f197.google.com [74.125.82.197]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 4chyv9j3yy-1 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NOT) for ; Wed, 25 Feb 2026 23:18:32 +0000 (GMT) Received: by mail-dy1-f197.google.com with SMTP id 5a478bee46e88-2bd3bf5dde4so208231eec.1 for ; Wed, 25 Feb 2026 15:18:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oss.qualcomm.com; s=google; t=1772061512; x=1772666312; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=k1ncu6ArYzJhC1oWtoKaTbf490HS3AonBnLenM3Jd0c=; b=dDPG/FO+X9HJHG8AuHicfZN59PVwA18AUcZGXFNa7eRTDEcB9U5cny5UxCdlqPsIs4 IZky7UXw8xFo9C2Zy8dZAspoiMH+ULrE74p0Fq83F6nNjDdkHlkE9wi/rXw4x2eU/61q 4Ky6dTCWho3WBoaap4Bp3yaFfkFxyDrItCG1pW4iRIzR6hnHzxXARoJ916uu6MGr1qtu gzfIXCV6TAnoPYpjkh83CzuXdFZzhXsptDeyar0khrBQfdnAmurr1q38vBVjAaKFoGXv AYJ7E0+qjDSKkBHjDY3casb6REutx8dbFK4hTPuwO+nRDIrOOGuFwa2KH+2FZa3ntN3g nrcw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772061512; x=1772666312; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=k1ncu6ArYzJhC1oWtoKaTbf490HS3AonBnLenM3Jd0c=; b=qLyPTbPyPMgtzOURI+mSAgnGsOW+BLkwmt9KFPGPuCC6bhs9Rc6TGfP0B4HQRBT6Xj lUBX/0RGgxlw28fSXPA4DtG8kYIchDQdq5p9dY/FIya9Bm8RhOS8sfZA7gNXvTHl2f7s 8GgyZldg1bbbRoKAfZUkEkSL3LJ3rRihsrAsTWGBQEogE+dRcOuzhChR6WGGnLj1oRBo Kusn/jt3Nuc1A6/pBupEm6uNdMGoDT3XCW+aEpfrMaQ3Wx7jFOXXUe1w4C4w7CNvZLCy UWTudAbzMkB/08/26doAdYSvR0wGmbpPi640XkfQgRDND8aHHNHjMzZcUuRKZkiFwN08 FxNA== X-Forwarded-Encrypted: i=1; AJvYcCWomwX90cxdCkgSNLBgTsJfLV1HckWMVvjJqfGgTkV8ErwKdovlaqMtrEFsPMQ0FSCSh+gLMu61YmSRaTE=@vger.kernel.org X-Gm-Message-State: AOJu0YxLGlLdlVj4B0QYJwCv4SsThSfukTgoVMuzOjOOJOfF7tOu92z1 MKp5c8sRi7N/7mqAjGkdZPzz3FRFQWtvnfTA1mHVtly3Now2bceK7o2cxwtysPImFi6d9ILZq3e J6od0XK0PItllxOvOQilLtCA+mHfm9BC8LYZXAx19SPoh/kQMmkteMRx3xfYK8gYb2uM= X-Gm-Gg: ATEYQzx0f1fA+h0j9cy+wBcu0Bd8cqDQq5PehRj88h57ATYR+0LirkCrEqWKP0nPsyB nfj3wsNJYLBs140rYyphMpNME0FcH2PKmVxKlYMOeUE4P4969C4PaYrkgpIBW1ylo/n1MttrBUF ni7sCdZIjFb6svJy/7j7/r4refcwG4tjaGd9GCNSHvqGZybpX7iuuaPTZYDxWP8/xlM1O/yoCgH 1JKKBwlsl048quLw8Grzc3Kz5dIjs8nnrAd5gpiUHUCUL8AU7wuAOmuFiSYlM7gd41cZuc4TgTr QDPgHylbQI8SP8p9r0zzzUoQKCaKl7HnY1rBidxLhTdtWaleOJo59bKjzPEBPReSjcwfwpjNA6v X//4zbjwFbfM5ovg6iPo9PMtkAHID80AxvZYh3lDrMfleDtnxpM4CRZ2GOOPm3Ka+JSr9WJ4zDz PTuCOm X-Received: by 2002:a05:7300:538e:b0:2b7:1abc:a6eb with SMTP id 5a478bee46e88-2bdcbf4440dmr892763eec.7.1772061511631; Wed, 25 Feb 2026 15:18:31 -0800 (PST) X-Received: by 2002:a05:7300:538e:b0:2b7:1abc:a6eb with SMTP id 5a478bee46e88-2bdcbf4440dmr892750eec.7.1772061510969; Wed, 25 Feb 2026 15:18:30 -0800 (PST) Received: from [10.134.65.116] (i-global254.qualcomm.com. [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-kernel@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: TuhINssfKHk20Hz-1HduX82LhdGc6F0J X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI1MDIyMiBTYWx0ZWRfXyZWfSgDayjpL +c1Fx7BtDZuboJ2L5fEx1806EC5IMXpiaRS2ejmvzOo2sTQfT7Y5W2yEax4ahFQnNFnac5OGZGU RmWqCaCp0mIOGJ/Ud3TXP638aVewC3LEoBcL8sDuhJyqWVcVT8WCiBRi5exwFBUWNOxbLQqkMmh QF3HI8F+JZM1qWzlWhjn1gEN3eB6bh8Q4VnO+Vmc54L78fc7c38Fc/dG499tPOeYmd0V9b5wVZ9 CG3ptISRo3lVS/2897QD9qC0yNw/4c/X+wnTVP4hbkMB3H6oliQf5KP4Tay/LwOiIyqeHQkQs/4 1QHTuFktaNY4ZKE3RRt16boKoWqpF4d78jnNj1f9vmGFjVjgUZlJj/pNk+FowVTD9tYAIf4lZxD PFdu43xa/XoSJ2dfrgJxhwx4sXLujFwaMdibB0ymAm61nmOZyPqoA6qgrsvmjCyyksyhIxRraKw /K8esbbaLGJrCw8WJ+A== X-Authority-Analysis: v=2.4 cv=GZwaXAXL c=1 sm=1 tr=0 ts=699f8348 cx=c_pps a=Uww141gWH0fZj/3QKPojxA==:117 a=JYp8KDb2vCoCEuGobkYCKw==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=rJkE3RaqiGZ5pbrm-msn:22 a=AmUwcyaVtIZmdcZSVHAA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=PxkB5W3o20Ba91AHUih5:22 X-Proofpoint-GUID: TuhINssfKHk20Hz-1HduX82LhdGc6F0J 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 spamscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 suspectscore=0 adultscore=0 clxscore=1015 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