[PATCH 3/4] drm/imx: imx-tve: probe DDC before claiming the connector is connected

[Dmitry Baryshkov]

imx-tve provides no detect callback, so its connector is always reported
as connected and always gets the drm_add_modes_noedid() fallback list,
whether or not anything is attached to the VGA output.

On an i.MX53 QSRB with the MCIMXHDMICARD fitted and nothing on VGA, the
fbdev client therefore lights up both CRTCs: HDMI on DI0 at its preferred
1920x1080 (148.5 MHz) and the phantom VGA output on DI1 at the 1024x768
fallback (65 MHz). Both DIs are ultimately clocked from PLL4 - DI0 via
di_pll4_podf, the TVE via tve_pred/tve_ext_sel - and every link
propagates rate changes, so the TVE reprograms PLL4 underneath the
already running DI0. DI0 stops generating valid timings, its IDMAC EOF
interrupt (which ipuv3-crtc uses as the vblank source) never arrives, and
every commit waits out its full 10 s:

  imx-drm display-subsystem: [drm] *ERROR* [CRTC:40:crtc-0] flip_done timed out

The TVE outputs have no hotplug detection, but a DDC response is decent
evidence that a display is attached. The connector is already registered
with its DDC adapter, so wire up drm_connector_helper_detect_from_ddc().
It reports the connector as disconnected when the DDC bus is there but
nothing answers on it, and falls back to unknown only for boards that
describe no ddc-i2c-bus at all, which keeps those working as before.

Fixes: fcbc51e54d2a ("staging: drm/imx: Add support for Television Encoder (TVEv2)")
Assisted-by: Claude:claude-opus-5
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/imx/ipuv3/imx-tve.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/imx/ipuv3/imx-tve.c b/drivers/gpu/drm/imx/ipuv3/imx-tve.c
index e861b8b9d8fa..11ac69561eb8 100644
--- a/drivers/gpu/drm/imx/ipuv3/imx-tve.c
+++ b/drivers/gpu/drm/imx/ipuv3/imx-tve.c
@@ -322,6 +322,7 @@ static const struct drm_connector_funcs imx_tve_connector_funcs = {
 static const struct drm_connector_helper_funcs imx_tve_connector_helper_funcs = {
 	.get_modes = imx_tve_connector_get_modes,
 	.mode_valid = imx_tve_connector_mode_valid,
+	.detect_ctx = drm_connector_helper_detect_from_ddc,
 };
 
 static const struct drm_encoder_helper_funcs imx_tve_encoder_helper_funcs = {

-- 
2.47.3