From: Jens Glathe <[email protected]> drm_edid_read_ddc() can return a structurally valid EDID from which drm_edid_connector_add_modes() still returns zero modes. This triggers the error:
[drm:msm_dp_bridge_get_modes [msm]] *ERROR* failed to get DP sink modes, rc=0 even though the link is ready. Since the EDID is only read once, this error persists and the display comes up with 640x480 resolution. Add a retry of drm_edid_read_ddc() inside get_modes() when the initial read produces no usable modes. The bad EDID is freed before retrying and container_of ensures access to the DDC channel. This directly addresses the observed "valid but empty/garbage" EDID case on flaky DP plugs and adapters. I tested this on a few of my "flaky" type-c to HDMI adapters and hubs, getting no "retry failed" messages and the desired resolution. Without the patch most plugs would result in 640x480 external display. Fixes: [5bea90ad9743d2] "drm/msm/dp: switch to struct drm_edid" Signed-off-by: Jens Glathe <[email protected]> --- drivers/gpu/drm/msm/dp/dp_panel.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c index 6bb021820d7c5..4f27c8129b0ef 100644 --- a/drivers/gpu/drm/msm/dp/dp_panel.c +++ b/drivers/gpu/drm/msm/dp/dp_panel.c @@ -327,11 +327,39 @@ u32 msm_dp_panel_get_mode_bpp(struct msm_dp_panel *msm_dp_panel, int msm_dp_panel_get_modes(struct msm_dp_panel *msm_dp_panel, struct drm_connector *connector) { + int modes; + int retry; + struct msm_dp_panel_private *panel; + if (!msm_dp_panel) { DRM_ERROR("invalid input\n"); return -EINVAL; } + panel = container_of(msm_dp_panel, struct msm_dp_panel_private, msm_dp_panel); + + if (msm_dp_panel->drm_edid) { + modes = drm_edid_connector_add_modes(connector); + if (modes > 0) + return modes; + + drm_edid_free(msm_dp_panel->drm_edid); + msm_dp_panel->drm_edid = NULL; + } + + for (retry = 0; retry < 5; retry++) { + usleep_range(20000, 25000); + msm_dp_panel->drm_edid = + drm_edid_read_ddc(connector, &panel->aux->ddc); + if (msm_dp_panel->drm_edid) + break; + + drm_dbg_dp(connector->dev, + "get_modes re-read attempt %d/5 failed\n", + retry + 1); + } + + drm_edid_connector_update(connector, msm_dp_panel->drm_edid); if (msm_dp_panel->drm_edid) return drm_edid_connector_add_modes(connector); --- base-commit: 7da7f07112610a520567421dd2ffcb51beaefbcc change-id: 20260531-drm_plug_flaky_edid-cc7743f6f909 Best regards, -- Jens Glathe <[email protected]>
