On Mon, Mar 13, 2017 at 10:53:23PM +0200, ville.syrjala@xxxxxxxxxxxxxxx wrote: > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > Apparently some DP sinks are a little nuts and cause HPD to drop > intermittently during modesets. This happens eg. on an ASUS PB287Q. > In oder to recover from this we can't really use the previous > connector status to determine if the link needs retraining, so let's > just ignore that piece of information and do the retrain > unconditionally. We do of course still check whether the link is > supposed to be running or not. > > To actually get read out the EDID and update things properly we > also need to nuke the goto out added by commit 7d23e3c37bb3 > ("drm/i915: Cleaning up intel_dp_hpd_pulse"). I'm actually not sure > why that was there. Perhaps to avoid an EDID read if the connector > status didn't appear to change, but that sort of thing is quite racy > and would have failed anyway if we failed to keep up with the > hotplugs (if we missed the HPD down in between two HPD ups). And > now that we take this codepath unconditionally we definitely need > to drop the goto as otherwise we would never do the EDID read. > > v2: Drop the goto that made us skip EDID reads entirely. Doh! > > Cc: stable@xxxxxxxxxxxxxxx > Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx> > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> > Reported-by: Palmer Dabbelt <palmer@xxxxxxxxxxx> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99766 > References: https://lists.freedesktop.org/archives/intel-gfx/2017-February/119779.html > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_dp.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c > index fd96a6cf7326..5c2f1b37b58f 100644 > --- a/drivers/gpu/drm/i915/intel_dp.c > +++ b/drivers/gpu/drm/i915/intel_dp.c > @@ -4634,16 +4634,22 @@ intel_dp_long_pulse(struct intel_connector *intel_connector) > */ > status = connector_status_disconnected; > goto out; > - } else if (connector->status == connector_status_connected) { > + } else { > /* > - * If display was connected already and is still connected > - * check links status, there has been known issues of > - * link loss triggerring long pulse!!!! > + * If display is now connected check links status, > + * there has been known issues of link loss triggerring > + * long pulse. > + * > + * Some sinks (eg. ASUS PB287Q) seem to perform some > + * weird HPD ping pong during modesets. So we can apparely s/apparely/apparently/ > + * end up with HPD going low during a modeset, and then > + * going back up soon after. And once that happens we must > + * retrain the link to get a picture. That's in case no > + * userspace component reacted to intermittent HPD dip. Makes sense as the retraining is only applied if the crtc was active (i.e. the connector was previously connected and trained). Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> -Chris -- Chris Wilson, Intel Open Source Technology Centre