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

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

Hello Damon,

On Thu Mar 26, 2026 at 10:15 AM CET, Damon Ding wrote:
> On 3/26/2026 3:25 PM, Liu Ying wrote:
>> Hi Luca,
>>
>> On Fri, Mar 20, 2026 at 11:46:15AM +0100, Luca Ceresoli wrote:
>>> The meaning of this flag may not be obvious at first sight.
>>>
>>> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
>>> ---
>>>   include/drm/bridge/dw_hdmi.h | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>
> First of all, these changes related to the DW HDMI controller work well
> when tested on RK3399 HDMI.

Great!

You'd be welcome to send your Tested-by: tag if you tested the series on
hardware, that would be useful.

However at this point I suggest to wait for v2, which I'm sending soon, and
test that. I added you in Cc for it.

>>> 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

> Therefore, it may be better to adapt the dw-hdmi drivers across all
> platforms to the bridge-connector architecture simultaneously.
>
> This would allow removing &dw_hdmi_plat_data.output_port and unify the
> setting of DRM_BRIDGE_ATTACH_NO_CONNECTOR during the attach stage.
> (Just as the Analogix DP driver does [0])
>
> [0]
> https://lore.kernel.org/all/20260319071452.1961274-1-damon.ding@rock-chips.com/

I agree converting all users is a good goal, but I disagree it should be
done simultaneously. There are various users of dw-hdmi, and converting one
having the hardware to test it was painful enough for me. Converting all of
them without testing on hardware would be a hell.

However I might be wrong. Having a precise list of all users, which ones
need to be converted, and whether they have any special detail to be taken
care of would be good to estimate the work to convert all users. Without
that I'd rather let users convert one by one and hopefully get rid of
legacy code eventually.

Best regards,
Luca

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