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

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Date: Fri, 1 Mar 2024 07:32:50 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Chris Goldsworthy <quic_cgoldswo@...cinc.com>,
 Georgi Djakov <djakov@...nel.org>
Cc: 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,
 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_sukadev@...cinc.com, quic_pdaly@...cinc.com, quic_sudaraja@...cinc.com
Subject: Re: [PATCH v5 1/7] dt-bindings: iommu: Add Qualcomm TBU bindings

On 29/02/2024 23:24, Chris Goldsworthy wrote:
> On Thu, Feb 29, 2024 at 10:09:34PM +0200, Georgi Djakov wrote:
>> Hi Krzysztof,
>>
>> On 29.02.24 19:53, Krzysztof Kozlowski wrote:
>>> On 26/02/2024 18:22, Georgi Djakov wrote:
>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/iommu/qcom,tbu.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Qualcomm TBU (Translation Buffer Unit)
>>>> +
>>>> +maintainers:
>>>> +  - Georgi Djakov <quic_c_gdjako@...cinc.com>
>>>> +
>>>> +description:
>>>> +  The Qualcomm SMMU500 implementation consists of TCU and TBU. The TBU contains
>>>> +  a Translation Lookaside Buffer (TLB) that caches page tables. TBUs provides
>>>> +  debug features to trace and trigger debug transactions. There are multiple TBU
>>>> +  instances with each client core.
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    const: qcom,qsmmuv500-tbu
>>>
>>> Why we don't have SoC specific compatibles? If that's for SDM845, then
>>> it should be qcom,sdm845-tbu or qcom,sdm845-qsmmuv500-tbu
>>>
>>
>> Because they should be all compatible (as registers). Adding a SoC compatible
>> might get overly-specific, but i can also see the benefits in that, so ok will
>> do it!
>>
> 
> Hi Krzysztof,
> 
> JFYI that the TBUs are used on our mobile SoCs going up until the SoC
> we commercialized in early 2022, Snapdragon 8 Gen 1. Including SDM845
> there are three more premium tier SoCs using TBUs plus all of their
> value-tier derivatives.  There will also be prior generation premium
> tier SoCs along with their derivatives that use the TBU as well. Does
> it make sense to have a target-specific compatible string given this? 

This does not explain me anything. Why an exemption from usual bindings
rules should apply here?

https://elixir.bootlin.com/linux/v6.8-rc6/source/Documentation/devicetree/bindings/writing-bindings.rst

Best regards,
Krzysztof