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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LH0YlKVC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LH0YlKVC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BEFFF1F00A3A; Mon, 7 Sep 2026 07:48:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788767296; bh=7xw1YjXu3NsISpbAsCe3ks3f4YjdNeeUrtEKLcKFtA4=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=LH0YlKVCPrnK7MTi2G1cu1ltPl2UuFvrSAfMD6jjEh9kF4GE79w2CNfRiMr6vUfk1 ru95sYEsVP7QdClnQpVDBEXMaUEDRG3d1GyV/jaaIiolbE5KeMGaDd1K6xAB2osOWJ IIHPyVLQ7kaxjb4ji6LVUQgmSM2FYl56/EhRVTVi8B+cBp/wRBaJ/5/1IltxczLyYf dp41Ss5PvBL72JTMnoTnwPSbcHpsmk+tHDMLPwQcncSqQfeOr0pLrTWXlNM8r+L0fI UYNDhKc4RgaukPphQJ2N8J9FKgEsZSEo48LoD02xfjkK66GthU0tUNIqUAWOO+eHmZ GQnHn9UVismsw== Message-ID: <23d6166f-50f7-4d23-a700-ab738c1e872f@kernel.org> Date: Mon, 7 Sep 2026 09:48:09 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] dt-bindings: sound: qcom,q6apm-dai: add stage-2 (SCM/VMID) access model From: Krzysztof Kozlowski To: Ajay Kumar Nandam , Srinivas Kandagatla , Liam Girdwood , Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Jaroslav Kysela , Takashi Iwai Cc: linux-sound@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260826-a2a-shikra-vmid-v5-v2-0-c3dc62354eee@oss.qualcomm.com> <20260826-a2a-shikra-vmid-v5-v2-1-c3dc62354eee@oss.qualcomm.com> <006617c6-e3b0-4a3b-85e5-6b5af8f11879@kernel.org> <51413da4-eed6-4251-b2eb-5d2ad8cb36ec@oss.qualcomm.com> Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 03/09/2026 11:39, Krzysztof Kozlowski wrote: > On 02/09/2026 08:07, Ajay Kumar Nandam wrote: >> >> >> On 8/27/2026 11:33 AM, Krzysztof Kozlowski wrote: >>> On 25/08/2026 20:40, Ajay Kumar Nandam wrote: >>>> The APM DAIs expose PCM buffers that the backing DSP must be able to >>>> reach. On existing targets the DSP runs in a stage-1 context and the >>>> buffers are described to the SMMU via the iommus property. >>>> >>>> On platforms such as Qualcomm Shikra, where audio is served by the modem >>>> DSP (mDSP) rather than the ADSP, the DSP runs in a stage-2 protected >>>> context and cannot use the SMMU. The buffers are reachable only after >>>> hypervisor (SCM) memory assignment to the fixed set of consumer Virtual >>>> Machine IDs (VMIDs) that own that protected context. Describe those >>>> consumers with a new qcom,vmids property. >>>> >>>> The two access models are mutually exclusive: a node carries either >>>> iommus (stage-1/SMMU) or qcom,vmids (stage-2/SCM), expressed with a >>>> oneOf constraint. iommus is therefore no longer unconditionally required. >>>> SCM assignment replaces the buffer's current owners with the supplied >>>> destination set, so the driver always adds HLOS to that set itself to >>>> retain host access; HLOS must not be listed in qcom,vmids. >>>> >>>> When qcom,vmids is present the PCM buffers must reside in reserved-memory >>>> carveouts that are SCM-assigned to the consumer VMIDs. Add an optional >>>> memory-region property listing those carveouts. The first entry is the >>>> control-path buffer and subsequent entries are data-path buffers. >>>> memory-region is only meaningful alongside qcom,vmids, enforced via >>>> dependentRequired. >>>> >>>> Signed-off-by: Ajay Kumar Nandam >>>> --- >>>> .../devicetree/bindings/sound/qcom,q6apm-dai.yaml | 72 +++++++++++++++++++++- >>>> 1 file changed, 70 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/Documentation/devicetree/bindings/sound/qcom,q6apm-dai.yaml b/Documentation/devicetree/bindings/sound/qcom,q6apm-dai.yaml >>>> index 9e5b30d9c6e6..d9a6bc4a14f2 100644 >>>> --- a/Documentation/devicetree/bindings/sound/qcom,q6apm-dai.yaml >>>> +++ b/Documentation/devicetree/bindings/sound/qcom,q6apm-dai.yaml >>>> @@ -10,7 +10,15 @@ maintainers: >>>> - Srinivas Kandagatla >>>> >>>> description: | >>>> - This binding describes the Qualcomm APM DAIs in DSP >>>> + This binding describes the Qualcomm APM DAIs in DSP. >>>> + >>>> + The DSP that runs the APM must be able to reach the PCM buffers. On >>>> + existing targets the DSP runs in a stage-1 context and the buffers are >>>> + described to the SMMU via iommus. On targets whose APM DSP runs in a >>>> + stage-2 protected context that cannot use the SMMU, the buffers are >>>> + reachable only after hypervisor (SCM) memory assignment to the fixed >>>> + set of consumer VMIDs that own that protected context, described by >>>> + qcom,vmids. The two access models are mutually exclusive. >>>> >>>> properties: >>>> compatible: >>>> @@ -20,9 +28,42 @@ properties: >>>> minItems: 1 >>>> maxItems: 2 >>> >>> As I said last time, different hardware, different programming >>> interface, different features, so a different compatible. >> >> >> The APM DAI block is the same packet format. The driver uses a single >> of_device_id entry with no match data; there is no code path dispatched >> by the compatible string. >> >> The iommu vs VMID distinction is a property of the memory topology, >> not the DAI hardware, and is already described by the mutually exclusive >> iommus / qcom,vmids properties. The DSP identity (ADSP vs mDSP) is >> carried by the GPR node's qcom,domain property and read at the send >> layer — the DAI node itself does not need to know which DSP it talks to. > > I am still trying to grasp it. You have a device "APM" and it accesses > PCM buffers or other memory in some way needing IOMMU for that. > > Now you add something which you call EXACTLY the same device, no > difference at all, same "APM", but this time this device operates > completely different, because it does not use IOMMU, but talks with > firmware via SCM. > > Well, I really do not see how is this still exactly the same or even > compatible device. > > The way device accesses its data is part of the programming model and > different programming models have different compatibles. Additionally, as explained to me in off-list channel, the qcom,vmids is not a hardware property at all (because hardware is the same), thus does not look suitable for DT. Best regards, Krzysztof