Re: [PATCH v2] drm/amd/display: Route connector DDC over AUX for native DP sinks

[Mario Limonciello <superm1@kernel.org>]

On 11/15/26 02:20, Wayne Lin wrote:
> Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>

Thanks Wayne.

Simon, Richard,

Can you please check that this resolves the issue raised?

Thanks,

> 
> On Tue, 03 Nov 2026 08:18:40 -0600, Mario Limonciello wrote:
>> On DisplayPort and eDP connectors DDC is tunneled over the AUX channel,
>> but the connector's "ddc" adapter ("AMDGPU DM i2c hw bus N") always
>> drives the physical i2c pins, which don't reach a native DP sink.  The
>> AUX backed adapter ("AMDGPU DM aux hw bus N") does, so userspace such as
>> fwupd, which uses the "ddc" sysfs link for DDC/CI, has to work around
>> this.
>>
>> Keep a single i2c bus per connector and pick the transport per transfer
>> based on the detected sink: if the sink is a native DP/eDP/MST sink,
>> forward the transfer to the AUX adapter, otherwise (DVI/HDMI, including
>> DP++ with a passive adapter) use the hw i2c engine as before.
>>
>> Reported-by: simonit.orig@gmail.com
>> Closes: https://github.com/fwupd/fwupd/pull/11308
>> Signed-off-by: Mario Limonciello <superm1@kernel.org>
>> ---
>> Changes in v2:
>> - Check which i2c bus to use on the fly instead of changing static symlink to
>>    avoid regressing passive adapters.
>> - Link to v1: https://patch.msgid.link/20261102-superm1-amdgpu-ddc-v1-1-9c5cb4a4f62d@amd.com
>> ---
>>   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c  | 16 ++++++++++++++++
>>   1 file changed, 16 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
>> index b498fc5fbb140..678caffa3d120 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
>> @@ -3373,6 +3373,22 @@ STATIC_IFN_KUNIT int amdgpu_dm_i2c_xfer(struct i2c_adapter *i2c_adap,
>>   	int i;
>>   	int result = -EIO;
>>   
>> +	if (!i2c->oem) {
>> +		struct dc_link *link = ddc_service->link;
>> +		struct amdgpu_dm_connector *aconnector = link->priv;
>> +
>> +		/*
>> +		 * DDC to a native DisplayPort sink is tunneled over the AUX
>> +		 * channel; the physical i2c pins only reach DVI/HDMI sinks
>> +		 * (e.g. DP++ with a passive adapter).  Route accordingly so
>> +		 * the connector's single "ddc" bus works for either sink.
>> +		 */
>> +		if (aconnector && link->local_sink &&
>> +		    dc_is_dp_signal(link->local_sink->sink_signal) &&
>> +		    aconnector->dm_dp_aux.aux.ddc.algo)
>> +			return i2c_transfer(&aconnector->dm_dp_aux.aux.ddc, msgs, num);
>> +	}
>> +
>>   	if (!ddc_service->ddc_pin)
>>   		return result;
>>   
>>
>> ---
>> base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
>> change-id: 20261102-superm1-amdgpu-ddc-63f0eb10c022
>>
>> Best regards,
>> --
>> Mario Limonciello <superm1@kernel.org>
>>
>>