linux-kernel - Re: [PATCH v3 02/12] dt-bindings: display: mediatek: add MT8195 hdmi bindings

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Date:   Mon, 2 Jan 2023 15:19:07 +0000
From:   Guillaume Ranquet <granquet@...libre.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        "oul@...nel.org" <vkoul@...nel.org>, CK Hu <ck.hu@...iatek.com>,
        "obh+dt@...nel.org" <robh+dt@...nel.org>,
        "kishon@...com" <kishon@...com>,
        Chunfeng Yun <Chunfeng.Yun@...iatek.com>,
        "hunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        Jitao Shi <jitao.shi@...iatek.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "atthias.bgg@...il.com" <matthias.bgg@...il.com>,
        ".zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "irlied@...il.com" <airlied@...il.com>,
        "zysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Mac Shen <Mac.Shen@...iatek.com>,
        "vicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "zysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        Stuart Lee <Stuart.Lee@...iatek.com>,
        "i-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "nux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "inux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH v3 02/12] dt-bindings: display: mediatek: add MT8195 hdmi bindings

On Mon, 02 Jan 2023 15:14, AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>Il 02/01/23 14:38, Guillaume Ranquet ha scritto:
>> On Mon, 26 Dec 2022 06:18, CK Hu (胡俊光) <ck.hu@...iatek.com> wrote:
>>> Hi, Guillaume:
>>>
>>> On Fri, 2022-11-04 at 15:09 +0100, Guillaume Ranquet wrote:
>>>> Add mt8195 SoC bindings for hdmi and hdmi-ddc
>>>>
>>>> On mt8195 the ddc i2c controller is part of the hdmi IP block and
>>>> thus has no
>>>> specific register range, power domain or interrupt, making it simpler
>>>> than its the legacy "mediatek,hdmi-ddc" binding.
>>>>
>>>> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
>>>> ---
>>>>
>>>
>>> [snip]
>>>
>>>> a/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-
>>>> hdmi-ddc.yaml
>>>> b/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-
>>>> hdmi-ddc.yaml
>>>> new file mode 100644
>>>> index 000000000000..2dc273689584
>>>> --- /dev/null
>>>> +++
>>>> b/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-
>>>> hdmi-ddc.yaml
>>>> @@ -0,0 +1,51 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id:
>>>> https://urldefense.com/v3/__http://devicetree.org/schemas/display/mediatek/mediatek,mt8195-hdmi-ddc.yaml*__;Iw!!CTRNKA9wMg0ARbw!wwVQuq5lzW0lvUFUkVXPWT8cIu96xdkn4tMams1E55qyxEZmgV1i0WfpOlq57w$
>>>>
>>>> +$schema:
>>>> https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!wwVQuq5lzW0lvUFUkVXPWT8cIu96xdkn4tMams1E55qyxEZmgV1i0WdSGOSxzw$
>>>>
>>>> +
>>>> +title: Mediatek HDMI DDC for mt8195
>>>> +
>>>> +maintainers:
>>>> +  - CK Hu <ck.hu@...iatek.com>
>>>> +  - Jitao shi <jitao.shi@...iatek.com>
>>>> +
>>>> +description: |
>>>> +  The HDMI DDC i2c controller is used to interface with the HDMI DDC
>>>> pins.
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - mediatek,mt8195-hdmi-ddc
>>>> +
>>>> +  clocks:
>>>> +    maxItems: 1
>>>> +
>>>> +  clock-names:
>>>> +    items:
>>>> +      - const: ddc
>>>> +
>>>> +  mediatek,hdmi:
>>>> +    $ref: /schemas/types.yaml#/definitions/phandle
>>>> +    description:
>>>> +      A phandle to the mt8195 hdmi controller
>>>> +
>>>> +required:
>>>> +  - compatible
>>>> +  - clocks
>>>> +  - clock-names
>>>> +
>>>> +additionalProperties: false
>>>> +
>>>> +examples:
>>>> +  - |
>>>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>>>> +    #include <dt-bindings/interrupt-controller/irq.h>
>>>> +    hdmiddc0: i2c {
>>>> +      compatible = "mediatek,mt8195-hdmi-ddc";
>>>> +      mediatek,hdmi = <&hdmi0>;
>>>> +      clocks = <&clk26m>;
>>>> +      clock-names = "ddc";
>>>> +    };
>>>
>>> I think we should not have a virtual device. This ddc is part of
>>> mt8195-hdmi device, so just keep mt8195-hdmi, and let mt8195-hdmi
>>> driver to probe the sub driver of ddc driver.
>>>
>>> Regards,
>>> CK
>>
>> Hi CK,
>>
>> Thx for your input.
>> Though I would strongly prefer to keep the ddc as a separate "virtual device".
>>
>> It aligns better with the goal of reusing as much code as possible
>> from the HDMI V1 IP,
>> which is something you have been advocating since V1 of this patch
>> quite some time ago
>> and has shaped this patch.
>>
>> To me we are in a state that is clean and avoids branching in the hdmi
>> common code.
>> Would you reconsider and allow the use of that virtual device?
>>
>> Thx,
>> Guillaume.
>>
>
>You can as well keep the DDC as a separated driver, but register in the HDMI v1 and
>v2 driver at probe time.
>
>Doing that, you won't need any devicetree node specific to any virtual device :-)
>
>Cheers,
>Angelo
>
>

Sure, but does it make any sense for HDMI v1?
As the ddc in v1 is a real device which (in theory) can be reused by other IPs.

I would see either v1 and v2 ddc exposed as a devicetree node (which
is what I favor).
Or v1 as a devicetree node and v2 probed directly from the hdmi code base.

Thx,
Guillaume.