Re: [Intel-gfx] [PATCH 01/14] drm/i915/tc: Abort DP AUX transfer on a disconnected TC port

[Imre Deak <imre.deak@intel.com>]

On Tue, Mar 21, 2023 at 01:09:41PM +0200, Kahola, Mika wrote:
> > -----Original Message-----
> > From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Imre
> > Deak
> > Sent: Thursday, March 16, 2023 3:17 PM
> > To: intel-gfx@lists.freedesktop.org
> > Cc: Chris Chiu <chris.chiu@canonical.com>
> > Subject: [Intel-gfx] [PATCH 01/14] drm/i915/tc: Abort DP AUX transfer on a
> > disconnected TC port
> >
> > On TC ports the 4ms AUX timeout combined with the 5 * 32 retry attempts
> > during DPCD accesses adds a 640ms delay to each access if the sink is
> > disconnected. This in turn slows down a modeset during which the sink is
> > disconnected (for instance a disabling modeset).
> >
> > Prevent the above delay by aborting AUX transfers on a TC port with a
> > disconnected sink.
> >
> > The DP 1.4a link CTS (4.2.1.5 Source Device Inactive HPD / Inactive AUX
> > Test") also requires not to initiate AUX transfers on disconnected DP ports in
> > general, however this patch doesn't change the behavior on non-TC ports,
> > leaving that for a follow-up.
> >
> > Reported-and-tested-by: Chris Chiu <chris.chiu@canonical.com>
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8279
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp_aux.c | 15 +++++++++++++--
> >  drivers/gpu/drm/i915/display/intel_tc.c     | 15 +++++++++++----
> >  drivers/gpu/drm/i915/display/intel_tc.h     |  1 +
> >  3 files changed, 25 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > index 96967e21c94c2..eb07dc5d87099 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> > @@ -205,8 +205,19 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
> >       for (i = 0; i < ARRAY_SIZE(ch_data); i++)
> >               ch_data[i] = intel_dp->aux_ch_data_reg(intel_dp, i);
> >
> > -     if (is_tc_port)
> > +     if (is_tc_port) {
> >               intel_tc_port_lock(dig_port);
> > +             /*
> > +              * Abort transfers on a disconnected port as required by
> > +              * DP 1.4a link CTS 4.2.1.5, also avoiding the long AUX
> > +              * timeouts that would otherwise happen.
> > +              * TODO: abort the transfer on non-TC ports as well.
> > +              */
> > +             if (!intel_tc_port_connected_locked(&dig_port->base)) {
> > +                     ret = -ENXIO;
> 
> TC port being a physical object this error code could be ENODEV as well, right?

The meaning of either error code is not defined precisely, but I
interpreted ENXIO as a - temporary - error/non-presence of the remote
device downstream of the port. There is another driver returning ENXIO
for the same case.

> Anyway, patch looks ok to me.
> 
> Reviewed-by: Mika Kahola <mika.kahola@intel.com>
> 
> > +                     goto out_unlock;
> > +             }
> > +     }
> >
> >       aux_domain = intel_aux_power_domain(dig_port);
> >
> > @@ -367,7 +378,7 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
> >
> >       intel_pps_unlock(intel_dp, pps_wakeref);
> >       intel_display_power_put_async(i915, aux_domain, aux_wakeref);
> > -
> > +out_unlock:
> >       if (is_tc_port)
> >               intel_tc_port_unlock(dig_port);
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_tc.c
> > b/drivers/gpu/drm/i915/display/intel_tc.c
> > index f45328712bff1..050f998284592 100644
> > --- a/drivers/gpu/drm/i915/display/intel_tc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_tc.c
> > @@ -768,16 +768,23 @@ void intel_tc_port_sanitize_mode(struct
> > intel_digital_port *dig_port)
> >   * connected ports are usable, and avoids exposing to the users objects they
> >   * can't really use.
> >   */
> > +bool intel_tc_port_connected_locked(struct intel_encoder *encoder) {
> > +     struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
> > +     struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
> > +
> > +     drm_WARN_ON(&i915->drm, !intel_tc_port_ref_held(dig_port));
> > +
> > +     return tc_port_live_status_mask(dig_port) & BIT(dig_port->tc_mode); }
> > +
> >  bool intel_tc_port_connected(struct intel_encoder *encoder)  {
> >       struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
> >       bool is_connected;
> >
> >       intel_tc_port_lock(dig_port);
> > -
> > -     is_connected = tc_port_live_status_mask(dig_port) &
> > -                    BIT(dig_port->tc_mode);
> > -
> > +     is_connected = intel_tc_port_connected_locked(encoder);
> >       intel_tc_port_unlock(dig_port);
> >
> >       return is_connected;
> > diff --git a/drivers/gpu/drm/i915/display/intel_tc.h
> > b/drivers/gpu/drm/i915/display/intel_tc.h
> > index d54082e2d5e8d..93813056043a5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_tc.h
> > +++ b/drivers/gpu/drm/i915/display/intel_tc.h
> > @@ -17,6 +17,7 @@ bool intel_tc_port_in_dp_alt_mode(struct
> > intel_digital_port *dig_port);  bool intel_tc_port_in_legacy_mode(struct
> > intel_digital_port *dig_port);
> >
> >  bool intel_tc_port_connected(struct intel_encoder *encoder);
> > +bool intel_tc_port_connected_locked(struct intel_encoder *encoder);
> >
> >  u32 intel_tc_port_get_lane_mask(struct intel_digital_port *dig_port);
> >  u32 intel_tc_port_get_pin_assignment_mask(struct intel_digital_port
> > *dig_port);
> > --
> > 2.37.1
>