[PATCH v2] drm/amd/display: Report non-DP display as disconnected without EDID

[Michel Dänzer]

On 2018-08-01 09:51 PM, Harry Wentland wrote:
> [Why]
> Some boards seem to have a problem where HPD is high on HDMI even though
> no display is connected. We don't want to report these as connected. DP
> spec still requires us to report DP displays as connected when HPD is
> high but we can't read the EDID in order to go to fail-safe mode.
> 
> [How]
> If connector_signal is not DP abort detection if we can't retrieve the
> EDID.
> 
> Bugzilla: https://bugs.freedesktop.org/107390
> Bugzilla: https://bugs.freedesktop.org/106846
> Cc: stable at vger.kernel.org
> Signed-off-by: Harry Wentland <harry.wentland at amd.com>
> Acked-by: Alex Deucher <alexander.deucher at amd.com>
> 
> v2: Add Bugzilla and stable
> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_link.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> index b180197a41e2..84f0fd15be4c 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> @@ -744,6 +744,17 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
>  			break;
>  		case EDID_NO_RESPONSE:
>  			DC_LOG_ERROR("No EDID read.\n");
> +
> +			/*
> +			 * Abort detection for non-DP connectors if we have
> +			 * no EDID
> +			 *
> +			 * DP needs to report as connected if HDP is high
> +			 * even if we have no EDID in order to go to
> +			 * fail-safe mode
> +			 */
> +			if (!dc_is_dp_signal(link->connector_signal))
> +				return false;
>  		default:
>  			break;
>  		}
> 

Could this be problematic with VGA connectors? AFAIR e.g. KVM switches
can cause trouble with retrieving EDID, or it could just be an old CRT
with no EDID in the first place.

Might it make sense to limit this to HDMI & DVI?


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer