Re: [PATCH 4/8] drm/bridge: dw-hdmi: document the output_port field

[Luca Ceresoli]

Hello Damon,

On Mon Mar 30, 2026 at 3:13 AM CEST, Damon Ding wrote:
>>>>> diff --git a/include/drm/bridge/dw_hdmi.h b/include/drm/bridge/dw_hdmi.h
>>>>> index 336f062e1f9d..45f6ba1a8ee1 100644
>>>>> --- a/include/drm/bridge/dw_hdmi.h
>>>>> +++ b/include/drm/bridge/dw_hdmi.h
>>>>> @@ -126,6 +126,11 @@ struct dw_hdmi_phy_ops {
>>>>>    struct dw_hdmi_plat_data {
>>>>>    	struct regmap *regm;
>>>>>
>>>>> +	/*
>>>>> +	 * The HDMI output port number (which must be 1) if it is described
>>>>
>>>> I'd rephrase:
>>>> The HDMI output port number must be 1 ...
>>>>
>>>
>>> Yes, the output port number should be 1, but I found that the output
>>> port number in the Rockchip-side dw-hdmi driver remains 0.
>>
>> Really? I checked all the bindings in
>> Documentation/devicetree/bindings/display/rockchip/*hdmi* and all mention
>> port@1 as the output port number. Can you point to code using port@0 as the
>> output port?
>>
>> Should it be true, that would be unfortunate because the output_port
>> variable does not handle this case. It's used as a sort of bool-or-int
>> variable:
>>
>>   * as a bool [0] to find out whether the DT is supposed to describe the
>>     output port
>>   * as an integer to tell the port number to parse in DT [1]
>>
>> So saying "please parse port 0" is impossible.
>>
>> [0] https://elixir.bootlin.com/linux/v7.0-rc5/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L3310
>> [1] https://elixir.bootlin.com/linux/v7.0-rc5/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L3315
>>
>
> Aha, my description might be a little misleading. The
> &dw_hdmi_plat_data.output_port is 0 on the Rockchip side, so the next
> bridge will not be parsed for it.
>
> Then I think the &dw_hdmi_plat_data.output_port should be 1, as this
> helps support the hdmi-connector and other bridge chips.

Ah, OK, that's all clear now.

> BTW: The Rockchip side dw-hdmi patches for bridge connector support will
> be updated as a follow-up to your patch series. :-)

Great! Don't forget to Cc me.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com