Re: [PATCH v3 1/2] dt-bindings: display: bridge: tc358867: Document default DP preemphasis

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi Marek,

Am Dienstag, 25. Juni 2024, 14:05:14 CEST schrieb Marek Vasut:
> Document default DP port preemphasis configurable via new DT property
> "toshiba,pre-emphasis". This is useful in case the DP link properties
> are known and starting link training from preemphasis setting of 0 dB
> is not useful. The preemphasis can be set separately for both DP lanes
> in range 0=0dB, 1=3.5dB, 2=6dB .
> 
> This is an endpoint property, not a port property, because the TC9595
> datasheet does mention that the DP might operate in some sort of split
> mode, where each DP lane is used to feed one display, so in that case
> there might be two endpoints.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
> Cc: Jonas Karlman <jonas@kwiboo.se>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Neil Armstrong <neil.armstrong@linaro.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Robert Foss <rfoss@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: devicetree@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: kernel@dh-electronics.com
> ---
> V2: - Fix the type to u8 array
>     - Fix the enum items to match what they represent
> V3: - Update commit message, expand on this being an endpoint property
> ---
>  .../display/bridge/toshiba,tc358767.yaml       | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml
> index 2ad0cd6dd49e0..9490854c22f3b 100644
> --- a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml
> +++ b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml
> @@ -98,6 +98,24 @@ properties:
>              reference to a valid eDP panel input endpoint node. This port is
>              optional, treated as DP panel if not defined
>  
> +        properties:
> +          endpoint:
> +            $ref: /schemas/media/video-interfaces.yaml#
> +            unevaluatedProperties: false
> +
> +            properties:
> +              toshiba,pre-emphasis:
> +                description:
> +                  Display port output Pre-Emphasis settings for both DP lanes.
> +                $ref: /schemas/types.yaml#/definitions/uint8-array
> +                minItems: 2
> +                maxItems: 2
> +                items:
> +                  enum:
> +                    - 0 # No pre-emphasis
> +                    - 1 # 3.5dB pre-emphasis
> +                    - 2 # 6dB pre-emphasis
> +
>      oneOf:
>        - required:
>            - port@0
> 

I get this warning:
> mx8mp-tqma8mpql-mba8mpxl.dtb: bridge@f: ports:port@2:endpoint: Unevaluated
> properties are not allowed ('toshiba,pre-emphasis' was unexpected)

DT node looks like this:

port@2 {
	reg = <2>;

	endpoint {
		toshiba,pre-emphasis = /bits/ 8 <1 1>;
	};
};

I think you are missing this change as well:
-- 8< --
--- a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml
+++ b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358767.yaml
@@ -92,7 +92,8 @@ properties:
             reference to a valid DPI output or input endpoint node.
 
       port@2:
-        $ref: /schemas/graph.yaml#/properties/port
+        $ref: /schemas/graph.yaml#/$defs/port-base
+        unevaluatedProperties: false
         description: |
             eDP/DP output port. The remote endpoint phandle should be a
             reference to a valid eDP panel input endpoint node. This port is
-- 8< --

How would you determine the values to be set here? I suspect it's the value
from register DP0_SnkLTChReq (0x6d4) after link training. Are they dependent
on the actual display to be attached?

Best regards,
Alexander
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