Re: [PATCH 7/8] drm/bridge: imx8mp-hdmi-tx: add an hdmi-connector when missing using a DT overlay at boot time

[Luca Ceresoli]

Hi Laurent,

On Thu Mar 26, 2026 at 9:28 AM CET, Laurent Pinchart wrote:

>> Many dts files for imx8mp-based boards in the kernel have such a connector
>> described and linked to port@1, so a connector is added by the
>> display-connector driver along with a bridge wrapping it. Sadly some of
>> those dts files don't have the connector described. Adding it would solve
>> the problem easily, but this would break existing devices which do not
>> update the dtb when upgrading to a newer kernel.
>
> I think this series should also fix the in-tree dts files, to pave the
> way for removing the workaround.

Fixing all dts files can surely be done, but it won't allow removing the
workaround. Any devices shipped with a dtb without the connector and
upgrading their kernel later on but not the dtb will fail as soon as they
upgrade to a kernel with patch 8 but with this workaround removed.

That said, do you still think it's worth adding the hdmi-connector node to
all dtbs missing it?

It should be fairly simple and IIRC it would involve a couple dozen drivers
at most based on my initial research. However for most of them I have no
way to know which type of connector is installed, would it be OK if we
describe type A when the type is unknown, just like
dw_hdmi_connector_create() does right now programmatically [0]?

[0] https://elixir.bootlin.com/linux/v7.0-rc5/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L2601

Also, if such a change is to be done, I'd definitely do it as a separate
series, to avoid adding more stuff to this series in-flight.

>> --- a/drivers/gpu/drm/bridge/imx/Kconfig
>> +++ b/drivers/gpu/drm/bridge/imx/Kconfig
>> @@ -25,6 +25,23 @@ config DRM_IMX8MP_DW_HDMI_BRIDGE
>>  	  Choose this to enable support for the internal HDMI encoder found
>>  	  on the i.MX8MP SoC.
>>
>> +config DRM_IMX8MP_DW_HDMI_BRIDGE_CONNECTOR_FIXUP
>> +	bool "Support device tree blobs without an hdmi-connector node"
>> +	default y
>
> Can't we enable the workaround unconditionally ? Distributions will need
> to enable this option anyway as they can't know what device they will
> boot on. I fear a configuration option will confuse users and waste time
> on debugging.

Sure, good point.

Luca

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