Re: [PATCH 07/12] drm/i915: Move DP link retraining into intel_dp_detect()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jul 28, 2016 at 12:48:53PM -0700, Manasi Navare wrote:
> On Thu, Jul 28, 2016 at 05:50:43PM +0300, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > DP link retraining needs to grab some modeset locks to not race with
> > modesets, so we can't really do it safely from the hpd_pulse, lest we
> > risk deadlocking due to MST sideband stuff.
> > 
> > Move the link retraining to happen from the hotplug work instead.
> > Doing at the end of intel_dp_detect() seems like a good place in case
> > the sink already got disconnected, in which case retraining is
> > pointless.
> > 
> > To determine if we need to schedule the hotplug work, we'll just check
> > the sink lane status without locks from hpd_pulse. A little racy
> > still eg. due to useing intel_dp->lane_count, but no less racy than
> > what we already had. We'll repeat the check in from intel_dp_detect()
> > with proper locking, where we'll also check if the link as actually
> > active or not.
> > 
> > Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
> > Cc: Jim Bride <jim.bride@linux.intel.com>
> > Cc: Manasi D Navare <manasi.d.navare@intel.com>
> > Cc: Durgadoss R <durgadoss.r@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 154 +++++++++++++++++-----------------------
> >  1 file changed, 66 insertions(+), 88 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 4a4184c21989..675b83f57a07 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3842,15 +3842,6 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> >  		bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
> >  go_again:
> >  		if (bret == true) {
> > -
> > -			/* check link status - esi[10] = 0x200c */
> > -			if (intel_dp->active_streams &&
> > -			    !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
> > -				DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
> > -				intel_dp_start_link_train(intel_dp);
> > -				intel_dp_stop_link_train(intel_dp);
> > -			}
> > -
> >  			DRM_DEBUG_KMS("got esi %3ph\n", esi);
> >  			ret = drm_dp_mst_hpd_irq(&intel_dp->mst_mgr, esi, &handled);
> >  
> > @@ -3886,34 +3877,42 @@ go_again:
> >  	return -EINVAL;
> >  }
> >  
> > -static void
> > -intel_dp_check_link_status(struct intel_dp *intel_dp)
> > +static bool
> > +intel_dp_link_needs_retrain(struct intel_dp *intel_dp)
> >  {
> > -	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
> > -	struct drm_device *dev = intel_dp_to_dev(intel_dp);
> >  	u8 link_status[DP_LINK_STATUS_SIZE];
> >  
> > -	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
> > +	if (intel_dp->active_streams == 0)
> > +		return false;
> > +
> > +	if (intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING)
> > +		return true;
> >  
> >  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
> >  		DRM_ERROR("Failed to get link status\n");
> > -		return;
> > +		return false;
> >  	}
> >  
> > -	if (!intel_encoder->base.crtc)
> > -		return;
> > +	return !drm_dp_channel_eq_ok(link_status, intel_dp->lane_count);
> 
> According to the DP spec, we should also check for the clock recovery bit in DPCD
> We should also add a check drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)

I think drm_dp_channel_eq_ok() checks all the bits: INTERLANE_ALIGN_DONE,
CR_DONE, EQ_DONE, and SYMBOL_LOCKED.

Anyways, while I was looking at the short pulse handling a bit more, I came
to the conclusion that we should rewrite it a bit.

The CTS docs seem to say that we're expected to read DPCD 0x200-0x205 on 
short pulse, and use that information to determine what we should do.
Currently we don't do that.

So I was thunking that we'd adjust the link_status stuff to read 0x200-0x207
instead of 0x202-0x207, like so:
-#define DP_LINK_STATUS_SIZE       6
+#define DP_LINK_STATUS_SIZE       8

 static u8 dp_link_status(const u8 link_status[DP_LINK_STATUS_SIZE], int r)
 {
-       return link_status[r - DP_LANE0_1_STATUS];
+       return link_status[r - DP_SINK_COUNT];
 }

And then we'd use something like this as our short pulse handler:

static bool
intel_dp_short_pulse(struct intel_dp *intel_dp)
{
        u8 link_status[DP_LINK_STATUS_SIZE], tmp;

        /*                                                                                                             
         * Clearing compliance test variables to allow capturing                                                       
         * of values for next automated test request.                                                                  
         */
        intel_dp->compliance_test_active = 0;
        intel_dp->compliance_test_type = 0;
        intel_dp->compliance_test_data = 0;

        if (!intel_dp_get_link_status(intel_dp, link_status))
                return false;

        tmp = drm_dp_link_status(link_status, DP_DEVICE_SERVICE_IRQ_VECTOR);
        if (tmp)
                drm_dp_dpcd_writeb(&intel_dp->aux,
                                   DP_DEVICE_SERVICE_IRQ_VECTOR,
                                   tmp);

        if (tmp & DP_AUTOMATED_TEST_REQUEST)
                DRM_DEBUG_DRIVER("Test request in short pulse not handled\n");
        if (tmp & (DP_CP_IRQ | DP_SINK_SPECIFIC_IRQ))
                DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");

        tmp = drm_dp_link_status(link_status, DP_LANE_ALIGN_STATUS_UPDATED);
        if (tmp & DP_DOWNSTREAM_PORT_STATUS_CHANGED)
                return false;

        tmp = drm_dp_link_status(link_status, DP_SINK_COUNT);
        if (DP_GET_SINK_COUNT(tmp) != intel_dp->sink_count)
                return false;

        if (intel_dp->active_streams != 0 &&
            !drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))
                return false;

        return true;
}

and obviously fill in whatever else sink irq handling we need.

Thoughts? Does that look sane?

<snip>
> >  
> >  static enum drm_connector_status
> >  intel_dp_detect(struct drm_connector *connector, bool force)
> >  {
> >  	struct intel_dp *intel_dp = intel_attached_dp(connector);
> > -	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> > -	struct intel_encoder *intel_encoder = &intel_dig_port->base;
> >  	struct intel_connector *intel_connector = to_intel_connector(connector);
> > +	enum drm_connector_status status;
> >  
> >  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
> >  		      connector->base.id, connector->name);
> >  
> > -	if (intel_dp->is_mst) {
> > -		/* MST devices are disconnected from a monitor POV */
> > -		intel_dp_unset_edid(intel_dp);
> > -		if (intel_encoder->type != INTEL_OUTPUT_EDP)
> > -			intel_encoder->type = INTEL_OUTPUT_DP;
> > -		return connector_status_disconnected;
> > -	}
> > -
> > -	/* If full detect is not performed yet, do a full detect */
> > -	if (!intel_dp->detect_done)
> > -		intel_dp_long_pulse(intel_dp->attached_connector);
> > +	status = intel_dp_long_pulse(intel_connector);
> >  
> > -	intel_dp->detect_done = false;
> > +	if (status == connector_status_connected || intel_dp->is_mst)
> 
> Whya re we not checking for (!intel_encoder->crtc.base) before retraining?
> I had seen issues with connected boot case when connector status is connected and if it
> tries to retrain it fails with retries because there is no active pipe. In that
> case it should not attempt to retrain.

I changed it to use intel_dp->active_streams instead. That'll work for MST
as well as SST. Checking for the crtc would only cover SST.

> 
> 
> > +		intel_dp_link_retrain(intel_dp);
> >  
> > -	if (is_edp(intel_dp) || intel_connector->detect_edid)
> > -		return connector_status_connected;
> > -	else
> > -		return connector_status_disconnected;
> > +	return status;
> >  }
> >  
> >  static void
> > @@ -4706,39 +4682,41 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >  		      port_name(intel_dig_port->port),
> >  		      long_hpd ? "long" : "short");
> >  
> > +	if (long_hpd)
> > +		return IRQ_NONE;
> > +
> >  	power_domain = intel_display_port_aux_power_domain(intel_encoder);
> >  	intel_display_power_get(dev_priv, power_domain);
> >  
> > -	if (long_hpd) {
> > -		intel_dp_long_pulse(intel_dp->attached_connector);
> > -		if (intel_dp->is_mst)
> > -			ret = IRQ_HANDLED;
> > -		goto put_power;
> > -
> > -	} else {
> > -		if (intel_dp->is_mst) {
> > -			if (intel_dp_check_mst_status(intel_dp) == -EINVAL) {
> > -				/*
> > -				 * If we were in MST mode, and device is not
> > -				 * there, get out of MST mode
> > -				 */
> > -				DRM_DEBUG_KMS("MST device may have disappeared %d vs %d\n",
> > -					      intel_dp->is_mst, intel_dp->mst_mgr.mst_state);
> > -				intel_dp->is_mst = false;
> > -				drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> > -								intel_dp->is_mst);
> > -				goto put_power;
> > -			}
> > -		}
> > -
> > -		if (!intel_dp->is_mst) {
> > -			if (!intel_dp_short_pulse(intel_dp)) {
> > -				intel_dp_long_pulse(intel_dp->attached_connector);
> > -				goto put_power;
> > -			}
> > +	if (intel_dp->is_mst) {
> > +		if (intel_dp_check_mst_status(intel_dp) == -EINVAL) {
> > +			/*
> > +			 * If we were in MST mode, and device is not
> > +			 * there, get out of MST mode
> > +			 */
> > +			DRM_DEBUG_KMS("MST device may have disappeared %d vs %d\n",
> > +				      intel_dp->is_mst, intel_dp->mst_mgr.mst_state);
> > +			intel_dp->is_mst = false;
> > +			drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> > +							intel_dp->is_mst);
> > +			goto put_power;
> >  		}
> > +	} else {
> > +		if (!intel_dp_short_pulse(intel_dp))
> > +			goto put_power;
> >  	}
> >  
> > +	/*
> > +	 * Link retraining happens from the hotplug work,
> > +	 * check if we might need to schdule it.
> > +	 *
> > +	 * There has been known issues of link loss
> > +	 * triggerring long pulse, so let's check both
> > +	 * for short and long pulse.
> > +	 */
> > +	if (intel_dp_link_needs_retrain(intel_dp))
> > +		goto put_power;
> > +
> >  	ret = IRQ_HANDLED;
> >  
> >  put_power:
> > -- 
> > 2.7.4
> > 

-- 
Ville Syrjälä
Intel OTC
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