linux-kernel - Re: [PATCH v5 1/7] dt-bindings: iommu: Add Qualcomm TBU bindings

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Message-ID: <ac88ea82-d541-4016-95ce-58388b1f86e7@kernel.org>
Date: Thu, 29 Feb 2024 22:17:23 +0200
From: Georgi Djakov <djakov@...nel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Georgi Djakov <quic_c_gdjako@...cinc.com>, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, will@...nel.org,
 robin.murphy@....com, joro@...tes.org, iommu@...ts.linux.dev
Cc: devicetree@...r.kernel.org, andersson@...nel.org,
 konrad.dybcio@...aro.org, robdclark@...il.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, quic_cgoldswo@...cinc.com,
 quic_sukadev@...cinc.com, quic_pdaly@...cinc.com, quic_sudaraja@...cinc.com
Subject: Re: [PATCH v5 1/7] dt-bindings: iommu: Add Qualcomm TBU bindings

Hi Krzysztof,

On 29.02.24 19:59, Krzysztof Kozlowski wrote:
> On 26/02/2024 18:22, Georgi Djakov wrote:
>> The "apps_smmu" on the Qualcomm sdm845 platform is an implementation
>> of the SMMU-500, that consists of a single TCU (Translation Control
>> Unit) and multiple TBUs (Translation Buffer Units). These TBUs have
>> hardware debugging features that are specific and only present on
>> Qualcomm hardware. Represent them as independent DT nodes. List all
>> the resources that are needed to operate them (such as registers,
>> clocks, power domains and interconnects).
>>
>> Signed-off-by: Georgi Djakov <quic_c_gdjako@...cinc.com>
>> ---
>>   .../devicetree/bindings/iommu/qcom,tbu.yaml   | 65 +++++++++++++++++++
>>   1 file changed, 65 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/iommu/qcom,tbu.yaml
> 
> Heh, I wonder how did you solve Robin's comments. I don't see you
> responding to Robin. Just v5 sent...

Yeah, i didn't respond because his response was clear to me. He responded
to the fundamental question whether to model the TBUs as child DT nodes of
the SMMU or as standalone nodes. So in the first versions of this patchset
we tried to explore the path with "child" nodes and search if there are any
other implementation than the Qualcomm one and try to find some common
binding... and Robin's objection was exactly to that. It seems that adding
more functionalities in TBUs (which requires resource management) is only
a Qualcomm thing and common binding does not make sense, so now we are
going with standalone DT nodes as he suggested.

Thanks,
Georgi