Hi Imre, > On Tue, May 24, 2022 at 11:29:54AM +0300, Kasireddy, Vivek wrote: > > Hi Imre, > > > > > 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. > > > > [Kasireddy, Vivek] I think it does after the first patch in this series is applied if > > the userspace (Weston) forces a modeset on a disconnected tc legacy port (HDMI). > > For instance, some of the FIA/PHY regs accesses I noticed include programming > > the lane count (intel_tc_port_set_fia_lane_count() called by intel_ddi_pre_pll_enable()), > > reading the pin assignment mask (intel_tc_port_get_pin_assignment_mask() called > > by icl_program_mg_dp_mode() which is called by intel_ddi_pre_enable_hdmi()), etc. > > The FW/HW will setup a legacy TC port's PHY once during system boot and > resume, so I don't see any problem modesetting those later, regardless > of a sink being plugged on them or not. We need the first patch which > fixes a bug selecting the wrong PLL. > > > Of-course, these accesses would probably not occur if the disconnected tc port > > defaults to TBT mode but this brings other problems like I described in the > > commit description of the first patch and the cover letter. > > > > > > > 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). > > > > [Kasireddy, Vivek] Regardless of whether the PHY/FIA regs are accessed or > > not, I don't think the driver should let the userspace's modeset to succeed on > > a disconnected tc port. Do you not agree? > > I don't think a modeset can or should be prevented if the user unplugs a > monitor midway. > > > > > 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. > > > > [Kasireddy, Vivek] Ok, assuming that the state of the sink is "connected" > > during intel_atomic_check() phase (which is where this patch checks for > > connected status), are you concerned about the case where the user may > > unplug the sink before we get to the intel_atomic_commit() phase? Is > > this what you meant when you said this earlier: "This check is racy, as > > right after dig_port->connected() returns true, the port can become > > disconnected"? I am just trying to figure out the scenarios when this > > might happen. > > Yes, checking the HPD live state and attempting to prevent a modeset > based on it doesn't work as this state can change at any moment. I don't > see a reason either why this should be done. > > > > > 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. > > > > [Kasireddy, Vivek] Right, that is the ideal case but user/userspace can commit > > mistakes where for example they can assume that HDMI-A-1 is connected > > (while it is not) instead of HDMI-A-3 which is the one actually connected. > > During such cases, I think the driver should not let the userspace hang the > > system or lead to unexpected states and instead should return an error. > > I can't see a problem modesetting a TC connector, when there is no sink > connected to it or the sink gets unplugged at an arbitrary time during > the modeset. [Kasireddy, Vivek] I think modesetting a TC connector with no sink connected would be equivalent to "using" it which is against what the spec says: "Display software must not use a disconnected port". Anyway, let me send a v2 of the first patch to include your suggestion. Thanks, Vivek > > --Imre
