On Fri, May 20, 2022 at 10:28:31AM +0300, Kasireddy, Vivek wrote: > Hi Imre, > [...] > > > > > @@ -131,6 +137,20 @@ int intel_digital_connector_atomic_check(struct drm_connector *conn, > > > > > > > > > > crtc_state = drm_atomic_get_new_crtc_state(state, new_state->crtc); > > > > > > > > > > + /* > > > > > + * The spec says that it is not safe to use a disconnected Type-C port. > > > > > + * Therefore, check to see if this connector is connected and reject > > > > > + * the modeset if there is no sink detected. > > > > > + */ > > > > > + if (dig_port && !dig_port->connected(encoder) && > > > > > > > > This check is racy, as right after dig_port->connected() returns true, > > > > the port can become disconnected. > > > > > > [Kasireddy, Vivek] Given that, do you think the only way to reliably determine > > > if the Type-C port has a sink is to check the live status and ignore dig_port->tc_mode? > > > > > > If that is the case, should I just add a function pointer to dig_port to call > > > tc_port_live_status_mask()? Or, should I just change intel_tc_port_connected() > > > to ignore dig_port->tc_mode like below: > > > @@ -764,8 +764,7 @@ bool intel_tc_port_connected(struct intel_encoder *encoder) > > > > > > intel_tc_port_lock(dig_port); > > > > > > - is_connected = tc_port_live_status_mask(dig_port) & > > > - BIT(dig_port->tc_mode); > > > + is_connected = tc_port_live_status_mask(dig_port); > > > > > > Or, are there any other elegant ways that you can think of to determine whether > > > a tc port has a sink or not? > > > > I meant that I don't think there is a way to prevent a modeset on a > > disconnected port. > > But we need to find a way right given that the spec clearly states that the driver > must not use or access (PHY/FIA registers of) a disconnected tc port. The driver does not access the PHY/FIA regs on a disconnected port/PHY. > > Live status is what provides the connected state, but > > it can change right after it is read out. > > Does this change happen after giving up the ownership (in > icl_tc_phy_disconnect)? The HPD live status changes whenever a user plugs/unplugs a sink. > But shouldn't we distinguish between the cases where we are > deliberately disconnecting the phy for power-savings reason vs when > the port actually becomes disconnected? The port can still be > considered connected in the former case right? The driver - based on the spec - needs to avoid accessing the PHY/FIA regs whenever the PHY is disconnected either by FW/HW (because the user unplugged the sink) or the driver (during the suspend, modeset disable sequence). > Under what other situations would the live status change or become > unreliable after the port has a connected sink? It's not unreliable, it reflects the state of a sink being plugged to the connector or not. > And, since we rely on SDEISR to detect the live status for tc legacy > ports, could this not be considered reliable? Changes in the HPD live status is used as a hint to user space to follow up with connector detection and modeset enable/disable requests as necessary. --Imre
