Re: [PATCH v2 1/2] dt-bindings: display: bridge: tc358867: Document default DP preemphasis

Marek Vasut
2024-06-23T16:39:55Z

On 6/22/24 1:56 PM, Conor Dooley wrote:
> On Fri, Jun 21, 2024 at 05:53:53PM +0200, Marek Vasut wrote:
>> 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 .
>>
>> Signed-off-by: Marek Vasut <marex@denx.de>
>> ---
>> V2: - Fix the type to u8 array
>> - Fix the enum items to match what they represent
>> ---
>> .../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..6287eb2b40908 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 ports.
>
> Why here and not in the port nodes?

There was a short discussion about that in V1:

https://lore.kernel.org/all/00e9ef90-3bbe-4556-8da9-462f65928781@denx.de/

"
Let's keep it in the endpoint node.

There is some mention in the TC9595 datasheet that the DP might operate
in some split mode, where each DP lane is used to feed one display (?),
so I assume in that case there might be two endpoints (?), but that is
not supported right now.

If that is ever needed, I guess this array would have minItems 1 and
maxItems 2 and another endpoint would be added to the schema for this
port 2.
"

>> + $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
>
> I'd love to say please make this -bB and put this in units, but that'd
> require it being a string..

I can do that. Do you think that's worth it ?