linux-kernel - Re: [PATCH 1/3] dt-bindings: display: msm: Add binding for MSM8996 DPU

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Message-ID: <384e2336-e6a3-28d6-4572-1534d418206b@linaro.org>
Date:   Sat, 30 Apr 2022 23:54:45 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>,
        ~postmarketos/upstreaming@...ts.sr.ht
Cc:     martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, jamipkettunen@...ainline.org,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: display: msm: Add binding for MSM8996
 DPU

On 30/04/2022 22:33, Dmitry Baryshkov wrote:
> On 30/04/2022 19:15, Konrad Dybcio wrote:
>> Add yaml binding for MSM8996 DPU.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...ainline.org>
>> ---
>>   .../bindings/display/msm/dpu-msm8996.yaml     | 221 ++++++++++++++++++
>>   1 file changed, 221 insertions(+)
>>   create mode 100644 
>> Documentation/devicetree/bindings/display/msm/dpu-msm8996.yaml
>>
>> diff --git 
>> a/Documentation/devicetree/bindings/display/msm/dpu-msm8996.yaml 
>> b/Documentation/devicetree/bindings/display/msm/dpu-msm8996.yaml
>> new file mode 100644
>> index 000000000000..10b02423224d
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/display/msm/dpu-msm8996.yaml
>> @@ -0,0 +1,221 @@
>> +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/display/msm/dpu-msm8996.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Qualcomm Display DPU dt properties for MSM8996 target
>> +
>> +maintainers:
>> +  - Konrad Dybcio <konrad.dybcio@...ainline.org>
>> +
>> +description: |
>> +  Device tree bindings for MSM Mobile Display Subsystem (MDSS) that
>> +  encapsulates sub-blocks like DPU display controller, DSI 
>> interfaces, etc.
>> +  Device tree bindings of MDSS and DPU are mentioned for MSM8996 target.
>> +
>> +properties:
>> +  compatible:
>> +    items:
>> +      - const: qcom,msm8996-mdss
> 
> With the unified MDSS driver there is no need to describe a separate 
> mdss bindings. Let's skip this part for now.
> 
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  reg-names:
>> +    const: mdss
>> +
>> +  power-domains:
>> +    maxItems: 1
>> +
>> +  clocks:
>> +    items:
>> +      - description: Display AHB clock
>> +      - description: Display core clock
>> +
>> +  clock-names:
>> +    items:
>> +      - const: iface
>> +      - const: core
>> +
>> +  interrupts:
>> +    maxItems: 1
>> +
>> +  interrupt-controller: true
>> +
>> +  "#address-cells": true
>> +
>> +  "#size-cells": true
>> +
>> +  "#interrupt-cells":
>> +    const: 1
>> +
>> +  iommus:
>> +    items:
>> +      - description: Phandle to mdp_smmu node with SID mask for 
>> Hard-Fail port0
>> +
>> +  ranges: true
>> +
>> +patternProperties:
>> +  "^display-controller@[0-9a-f]+$":
>> +    type: object
>> +    description: Node containing the properties of DPU.
>> +
>> +    properties:
>> +      compatible:
>> +        items:
>> +          - const: qcom,msm8996-dpu
> 
> Okay. So, this is the most interesting part. Unlike MSM8998, which is 
> supported in the mdp5 driver, but was not used in the upstream DTS 
> files, for the MSM8996 the MDP5 part is described, used and widely 
> tested. And, unfortunately, the bindings use solely the generic 
> "qcom,mdp5" compat.
> 
> I would suggest the following plan:
> - Define a binding using both "qcom,msm8996-dpu" and "qcom,mdp5" 
> strings. Make sure that it is fully backwards-compatible with older dts.
> 
> - Update msm8996.dtsi to follow new binding.
> 
> - Let's have a Kconfig flip switch selecting which driver to be used for 
> 8996/8998.

Rob suggested a modparam here.


-- 
With best wishes
Dmitry