linux-kernel - Re: [PATCH v1 2/7] dt-bindings: display: mediatek: Add binding for MT8195 HDMI-TX v2

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Message-ID: <3d5f7106-6425-420c-abac-39feed11c95c@collabora.com>
Date: Thu, 28 Nov 2024 11:32:13 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>,
 "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
Cc: "linux-mediatek@...ts.infradead.org"
 <linux-mediatek@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "tzimmermann@...e.de" <tzimmermann@...e.de>,
 "simona@...ll.ch" <simona@...ll.ch>, "mripard@...nel.org"
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Subject: Re: [PATCH v1 2/7] dt-bindings: display: mediatek: Add binding for
 MT8195 HDMI-TX v2

Il 28/11/24 07:02, CK Hu (胡俊光) ha scritto:
> Hi, Angelo:
> 
> On Wed, 2024-11-20 at 13:45 +0100, AngeloGioacchino Del Regno wrote:
>> External email : Please do not click links or open attachments until you have verified the sender or the content.
>>
>>
>> Add a binding for the HDMI TX v2 Encoder found in MediaTek MT8195
>> and MT8188 SoCs.
>>
>> This fully supports the HDMI Specification 2.0b, hence it provides
>> support for 3D-HDMI, Polarity inversion, up to 16 bits Deep Color,
>> color spaces including RGB444, YCBCR420/422/444 (ITU601/ITU709) and
>> xvYCC, with output resolutions up to 3840x2160p@...z.
>>
>> Moreover, it also supports HDCP 1.4 and 2.3, Variable Refresh Rate
>> (VRR) and Consumer Electronics Control (CEC).
>>
>> This IP also includes support for HDMI Audio, including IEC60958
>> and IEC61937 SPDIF, 8-channel PCM, DSD, and other lossless audio
>> according to HDMI 2.0.
>>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>   .../mediatek/mediatek,mt8195-hdmi.yaml        | 150 ++++++++++++++++++
>>   1 file changed, 150 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-hdmi.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-hdmi.yaml b/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-hdmi.yaml
>> new file mode 100644
>> index 000000000000..273a8871461e
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/display/mediatek/mediatek,mt8195-hdmi.yaml
>> @@ -0,0 +1,150 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: https://urldefense.com/v3/__http://devicetree.org/schemas/display/mediatek/mediatek,mt8195-hdmi.yaml*__;Iw!!CTRNKA9wMg0ARbw!lu0D_C3TwQ2-02jWYABnMIQ8vEoUwP0O4gbQndJnPUMpdi6wXdAHra9ivCfB7zoelDI7qsS20YdRlmP4bEKAABletXFX$
>> +$schema: https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!lu0D_C3TwQ2-02jWYABnMIQ8vEoUwP0O4gbQndJnPUMpdi6wXdAHra9ivCfB7zoelDI7qsS20YdRlmP4bEKAAFlnY-KY$
>> +
>> +title: MediaTek HDMI-TX v2 Encoder
>> +
>> +maintainers:
>> +  - AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> +  - CK Hu <ck.hu@...iatek.com>
>> +
>> +description: |
>> +  The MediaTek HDMI-TX v2 encoder can generate HDMI format data based on
>> +  the HDMI Specification 2.0b.
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - mediatek,mt8188-hdmi-tx
>> +      - mediatek,mt8195-hdmi-tx
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  interrupts:
>> +    maxItems: 1
>> +
>> +  clocks:
>> +    items:
>> +      - description: HDMI APB clock
>> +      - description: HDCP top clock
>> +      - description: HDCP reference clock
>> +      - description: VPP HDMI Split clock
> 
> I would like to know more about HDMI v2.
> Would you map each v2 clock to v1 clock?
> If one clock has no mapping, is it a new feature that v1 does not has?
> 

The HDMIv2 HW block seems to be almost completely different from the v1, and
it is also interconnected in a different way compared to MT8173 (the path goes
through VPP1, while the v1 is just direct to DPI/MMSYS).

The v1 block had specific clocks for the audio (i2s, I believe) and for the SPDIF,
and I have no idea how v1 does HDCP, but I don't see any specific clock for that.

The v2 block is clocked from the HDCP clock, the (apb) bus has its own clock, and
the video out needs the vpp split clock.

It's just different, and we can't shove the v2 binding inside of the v1 one, but
even if we could, since the v2 block is *that much* different from v1, it'd be a
mistake to do so.

Since the binding describes hardware, and since this v2 HW is *very* different
from v1, it needs a new binding document, that is true even if you find a way to
get the clocks to match (which is not possible, anyway).

Cheers,
Angelo

> Regards,
> CK
> 
>> +
>> +  clock-names:
>> +    items:
>> +      - const: bus
>> +      - const: hdcp
>> +      - const: hdcp24m
>> +      - const: hdmi-split
>> +
>>
>> --
>> 2.47.0
>>