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@cerno.tech --- drivers/gpu/drm/drm_scdc_helper.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/drm_scdc_helper.c b/drivers/gpu/drm/drm_scdc_helper.c index 48a382464d54..12e09fe8c8df 100644 --- a/drivers/gpu/drm/drm_scdc_helper.c +++ b/drivers/gpu/drm/drm_scdc_helper.c @@ -34,6 +34,19 @@ * 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 place to restore that state is + * in drm_encoder_helper_funcs.detect() or + * drm_connector_helper_funcs.detect_ctx(). */
#define SCDC_I2C_SLAVE_ADDRESS 0x54