There's some interactions between the SCDC setup and the disconnection / reconnection of displays. Let's document it and a solution. Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx> --- drivers/gpu/drm/display/drm_scdc_helper.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c b/drivers/gpu/drm/display/drm_scdc_helper.c index 81881e81ceae..c3ad4ab2b456 100644 --- a/drivers/gpu/drm/display/drm_scdc_helper.c +++ b/drivers/gpu/drm/display/drm_scdc_helper.c @@ -35,6 +35,19 @@ * HDMI 2.0 specification. It is a point-to-point protocol that allows the * HDMI source and HDMI sink to exchange data. The same I2C interface that * is used to access EDID serves as the transport mechanism for SCDC. + * + * Note: The SCDC status is going to be lost when the display is + * disconnected. This can happen physically when the user disconnects + * the cable, but also when a display is switched on (such as waking up + * a TV). + * + * This is further complicated by the fact that, upon a disconnection / + * reconnection, KMS won't change the mode on its own. This means that + * one can't just rely on setting the SCDC status on enable, but also + * has to track the connector status changes using interrupts and + * restore the SCDC status. The typical solution for this is to trigger an + * empty modeset in drm_connector_helper_funcs.detect_ctx(), like what vc4 does + * in vc4_hdmi_reset_link(). */ #define SCDC_I2C_SLAVE_ADDRESS 0x54 -- 2.37.1
