linux-kernel - Re: [PATCH v10 01/21] dt-bindings: mediatek,dpi: Add DPINTF compatible

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Date:   Wed, 25 May 2022 13:55:11 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Guillaume Ranquet <granquet@...libre.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, Helge Deller <deller@....de>,
        CK Hu <ck.hu@...iatek.com>, Jitao shi <jitao.shi@...iatek.com>
Cc:     Markus Schneider-Pargmann <msp@...libre.com>,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-phy@...ts.infradead.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v10 01/21] dt-bindings: mediatek,dpi: Add DPINTF
 compatible

Il 23/05/22 12:47, Guillaume Ranquet ha scritto:
> From: Markus Schneider-Pargmann <msp@...libre.com>
> 
> DPINTF is similar to DPI but does not have the exact same feature set
> or register layouts.
> 
> DPINTF is the sink of the display pipeline that is connected to the
> DisplayPort controller and encoder unit. It takes the same clocks as
> DPI.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> ---
>   .../bindings/display/mediatek/mediatek,dpi.yaml     | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.yaml b/Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.yaml
> index dd2896a40ff0..6d9f6c11806e 100644
> --- a/Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.yaml
> +++ b/Documentation/devicetree/bindings/display/mediatek/mediatek,dpi.yaml
> @@ -4,16 +4,16 @@
>   $id: http://devicetree.org/schemas/display/mediatek/mediatek,dpi.yaml#
>   $schema: http://devicetree.org/meta-schemas/core.yaml#
>   
> -title: mediatek DPI Controller Device Tree Bindings
> +title: mediatek DPI/DPINTF Controller
>   
>   maintainers:
>     - CK Hu <ck.hu@...iatek.com>
>     - Jitao shi <jitao.shi@...iatek.com>
>   
>   description: |
> -  The Mediatek DPI function block is a sink of the display subsystem and
> -  provides 8-bit RGB/YUV444 or 8/10/10-bit YUV422 pixel data on a parallel
> -  output bus.
> +  The Mediatek DPI and DPINTF function blocks are a sink of the display
> +  subsystem and provides 8-bit RGB/YUV444 or 8/10/10-bit YUV422 pixel data on a
> +  parallel output bus.
>   
>   properties:
>     compatible:
> @@ -23,6 +23,7 @@ properties:
>         - mediatek,mt8173-dpi
>         - mediatek,mt8183-dpi
>         - mediatek,mt8192-dpi
> +      - mediatek,mt8195-dpintf
>   
>     reg:
>       maxItems: 1
> @@ -35,12 +36,14 @@ properties:
>         - description: Pixel Clock
>         - description: Engine Clock
>         - description: DPI PLL
> +      - description: Optional CK CG Clock
>   
>     clock-names:
>       items:
>         - const: pixel
>         - const: engine
>         - const: pll
> +      - const: ck_cg

This is my understanding on how the DisplayPort Interface clocks work on 8195:

The "engine" clock is for the *VPP Engine's DisplayPort ip/block*,
"pll" is for TVD PLL divider selection
"pixel" is the gate for the pixel clock to the connected display.

"ck_cg" is useless, as that's the parent of "pixel" (and will always be)... for
example, on mt8195... check clk/mediatek/clk-mt8195-vdo0.c - the
CLK_VDO0_DP_INTF0_DP_INTF clock already has CLK_TOP_EDP as its parent, hence
enabling the first will enable the latter.

That said... you can most probably avoid adding the ck_cg clock, as if you try
to turn that off while it's in use by its children, you'll be only decrementing
a refcount, but no "real action" will ever take place.


Regards,
Angelo