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drm/amd/display: Use DAC load detection on analog connectors (v2)

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This feature is useful for analog connections without EDID:
- Really old monitors with a VGA connector
- Cheap DVI/VGA adapters that don't connect DDC pins

When a connection is established through DAC load detection,
the driver is supposed to fill in the supported modes for the
display, which we already do in amdgpu_dm_connector_get_modes.

Also, because the load detection causes visible glitches, do not
attempt to poll the connector again after it was detected this
way. Note that it will still be polled after sleep/resume or
when force is enabled, which is okay.

v2:
Add dc_connection_dac_load connection type.
Properly release sink when no display is connected.
Don't print error when EDID isn't read from an analog display.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Timur Kristóf 2025-09-26 20:02:00 +02:00 committed by Alex Deucher
parent d75e45b853
commit ac1bb49522
3 changed files with 72 additions and 2 deletions
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10
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
View File

@ -7248,6 +7248,16 @@ amdgpu_dm_connector_poll(struct amdgpu_dm_connector *aconnector, bool force)
enum dc_connection_type conn_type = dc_connection_none;
enum drm_connector_status status = connector_status_disconnected;
/* When we determined the connection using DAC load detection,
* do NOT poll the connector do detect disconnect because
* that would run DAC load detection again which can cause
* visible visual glitches.
*
* Only allow to poll such a connector again when forcing.
*/
if (!force && link->local_sink && link->type == dc_connection_dac_load)
return connector->status;
mutex_lock(&aconnector->hpd_lock);
if (dc_link_detect_connection_type(aconnector->dc_link, &conn_type) &&

3
drivers/gpu/drm/amd/display/dc/dc_types.h
View File

@ -353,7 +353,8 @@ enum dc_connection_type {
dc_connection_none,
dc_connection_single,
dc_connection_mst_branch,
dc_connection_sst_branch
dc_connection_sst_branch,
dc_connection_dac_load
};
struct dc_csc_adjustments {

61
drivers/gpu/drm/amd/display/dc/link/link_detection.c
View File

@ -904,6 +904,37 @@ static bool link_detect_ddc_probe(struct dc_link *link)
return true;
}
/**
* link_detect_dac_load_detect() - Performs DAC load detection.
*
* Load detection can be used to detect the presence of an
* analog display when we can't read DDC. This causes a visible
* visual glitch so it should be used sparingly.
*/
static bool link_detect_dac_load_detect(struct dc_link *link)
{
struct dc_bios *bios = link->ctx->dc_bios;
struct link_encoder *link_enc = link->link_enc;
enum engine_id engine_id = link_enc->preferred_engine;
enum dal_device_type device_type = DEVICE_TYPE_CRT;
enum bp_result bp_result;
uint32_t enum_id;
switch (engine_id) {
case ENGINE_ID_DACB:
enum_id = 2;
break;
case ENGINE_ID_DACA:
default:
engine_id = ENGINE_ID_DACA;
enum_id = 1;
break;
}
bp_result = bios->funcs->dac_load_detection(bios, engine_id, device_type, enum_id);
return bp_result == BP_RESULT_OK;
}
/*
* detect_link_and_local_sink() - Detect if a sink is attached to a given link
*
@ -1118,7 +1149,30 @@ static bool detect_link_and_local_sink(struct dc_link *link,
DC_LOG_ERROR("Partial EDID valid, abandon invalid blocks.\n");
break;
case EDID_NO_RESPONSE:
/* Analog connectors without EDID:
* - old monitor that actually doesn't have EDID
* - cheap DVI-A cable or adapter that doesn't connect DDC
*/
if (dc_connector_supports_analog(link->link_id.id)) {
/* If we didn't do DAC load detection yet, do it now
* to verify there really is a display connected.
*/
if (link->type != dc_connection_dac_load &&
!link_detect_dac_load_detect(link)) {
if (prev_sink)
dc_sink_release(prev_sink);
link_disconnect_sink(link);
return false;
}
DC_LOG_INFO("%s detected analog display without EDID\n", __func__);
link->type = dc_connection_dac_load;
sink->edid_caps.analog = true;
break;
}
DC_LOG_ERROR("No EDID read.\n");
/*
* Abort detection for non-DP connectors if we have
* no EDID
@ -1307,6 +1361,11 @@ static bool link_detect_analog(struct dc_link *link, enum dc_connection_type *ty
return true;
}
if (link_detect_dac_load_detect(link)) {
*type = dc_connection_dac_load;
return true;
}
*type = dc_connection_none;
return true;
}
@ -1328,7 +1387,7 @@ bool link_detect_connection_type(struct dc_link *link, enum dc_connection_type *
}
/* Ignore the HPD pin (if any) for analog connectors.
* Instead rely on DDC.
* Instead rely on DDC and DAC.
*
* - VGA connectors don't have any HPD at all.
* - Some DVI-A cables don't connect the HPD pin.