[Intel-gfx] [PATCH v3 3/3] drm/i915/dp_mst: Work around out-of-spec adapters filtering short pulses
Lyude Paul
lyude at redhat.com
Tue Jun 9 15:58:18 UTC 2020
Hi! Awesome patch series!
Reviewed-by: Lyude Paul <lyude at redhat.com>
Also re merging via drm-intel-next-queued - I think that should be fine, fwiw
merging via drm-misc-next might be another option (I've definitely done this in
the past for series that touched MST and drivers, but I don't have a hard
preference either way).
On Tue, 2020-06-09 at 15:15 +0300, Imre Deak wrote:
> Hi Dave, Lyude,
>
> are you ok to merge this patchset via the drm-intel-next-queued tree?
>
> --Imre
>
> On Thu, Jun 04, 2020 at 09:45:00PM +0300, Imre Deak wrote:
> > Some TypeC -> native DP adapters, at least the Club 3D CAC-1557 adapter,
> > incorrectly filter out HPD short pulses with a duration less than
> > ~540 usec, leading to MST probe failures.
> >
> > According to the DP Standard 2.0 section 5.1.4:
> > - DP sinks should generate short pulses in the 500 usec -> 1 msec range
> > - DP sources should detect short pulses in the 250 usec -> 2 msec range
> >
> > According to the DP Alt Mode on TypeC Standard section 3.9.2, adapters
> > should detect and forward short pulses according to how sources should
> > detect them as specified in the DP Standard (250 usec -> 2 msec).
> >
> > Based on the above filtering out short pulses with a duration less than
> > 540 usec is incorrect.
> >
> > To make such adapters work add support for a driver polling on MST
> > inerrupt flags, and wire this up in the i915 driver. The sink can clear
> > an interrupt it raised after 110 msec if the source doesn't respond, so
> > use a 50 msec poll period to avoid missing an interrupt. Polling of the
> > MST interrupt flags is explicitly allowed by the DP Standard.
> >
> > This fixes MST probe failures I saw using this adapter and a DELL U2515H
> > monitor.
> >
> > v2:
> > - Fix the wait event timeout for the no-poll case.
> > v3 (Ville):
> > - Fix the short pulse duration limits in the commit log prescribed by the
> > DP Standard.
> > - Add code comment explaining why/how polling is used.
> > - Factor out a helper to schedule the port's hpd irq handler and move it
> > to the rest of hotplug handlers.
> > - Document the new MST callback.
> > - s/update_hpd_irq_state/poll_hpd_irq/
> >
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> > drivers/gpu/drm/drm_dp_mst_topology.c | 32 ++++++++++++++++++--
> > drivers/gpu/drm/i915/display/intel_dp_mst.c | 10 ++++++
> > drivers/gpu/drm/i915/display/intel_hotplug.c | 18 +++++++++++
> > drivers/gpu/drm/i915/display/intel_hotplug.h | 2 ++
> > include/drm/drm_dp_mst_helper.h | 9 ++++++
> > 5 files changed, 68 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 5bc72e800b85..2a309fb2c4cc 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -1178,11 +1178,37 @@ static int drm_dp_mst_wait_tx_reply(struct
> > drm_dp_mst_branch *mstb,
> > struct drm_dp_sideband_msg_tx *txmsg)
> > {
> > struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> > + unsigned long wait_timeout = msecs_to_jiffies(4000);
> > + unsigned long wait_expires = jiffies + wait_timeout;
> > int ret;
> >
> > - ret = wait_event_timeout(mgr->tx_waitq,
> > - check_txmsg_state(mgr, txmsg),
> > - (4 * HZ));
> > + for (;;) {
> > + /*
> > + * If the driver provides a way for this, change to
> > + * poll-waiting for the MST reply interrupt if we didn't receive
> > + * it for 50 msec. This would cater for cases where the HPD
> > + * pulse signal got lost somewhere, even though the sink raised
> > + * the corresponding MST interrupt correctly. One example is the
> > + * Club 3D CAC-1557 TypeC -> DP adapter which for some reason
> > + * filters out short pulses with a duration less than ~540 usec.
> > + *
> > + * The poll period is 50 msec to avoid missing an interrupt
> > + * after the sink has cleared it (after a 110msec timeout
> > + * since it raised the interrupt).
> > + */
> > + ret = wait_event_timeout(mgr->tx_waitq,
> > + check_txmsg_state(mgr, txmsg),
> > + mgr->cbs->poll_hpd_irq ?
> > + msecs_to_jiffies(50) :
> > + wait_timeout);
> > +
> > + if (ret || !mgr->cbs->poll_hpd_irq ||
> > + time_after(jiffies, wait_expires))
> > + break;
> > +
> > + mgr->cbs->poll_hpd_irq(mgr);
> > + }
> > +
> > mutex_lock(&mgr->qlock);
> > if (ret > 0) {
> > if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > index d18b406f2a7d..9be52643205d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > @@ -33,6 +33,7 @@
> > #include "intel_connector.h"
> > #include "intel_ddi.h"
> > #include "intel_display_types.h"
> > +#include "intel_hotplug.h"
> > #include "intel_dp.h"
> > #include "intel_dp_mst.h"
> > #include "intel_dpio_phy.h"
> > @@ -765,8 +766,17 @@ static struct drm_connector
> > *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
> > return NULL;
> > }
> >
> > +static void
> > +intel_dp_mst_poll_hpd_irq(struct drm_dp_mst_topology_mgr *mgr)
> > +{
> > + struct intel_dp *intel_dp = container_of(mgr, struct intel_dp, mst_mgr);
> > +
> > + intel_hpd_trigger_irq(dp_to_dig_port(intel_dp));
> > +}
> > +
> > static const struct drm_dp_mst_topology_cbs mst_cbs = {
> > .add_connector = intel_dp_add_mst_connector,
> > + .poll_hpd_irq = intel_dp_mst_poll_hpd_irq,
> > };
> >
> > static struct intel_dp_mst_encoder *
> > diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c
> > b/drivers/gpu/drm/i915/display/intel_hotplug.c
> > index 4f6f560e093e..664f88354101 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hotplug.c
> > +++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
> > @@ -347,6 +347,24 @@ static void i915_digport_work_func(struct work_struct
> > *work)
> > }
> > }
> >
> > +/**
> > + * intel_hpd_trigger_irq - trigger an hpd irq event for a port
> > + * @dig_port: digital port
> > + *
> > + * Trigger an HPD interrupt event for the given port, emulating a short
> > pulse
> > + * generated by the sink, and schedule the dig port work to handle it.
> > + */
> > +void intel_hpd_trigger_irq(struct intel_digital_port *dig_port)
> > +{
> > + struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
> > +
> > + spin_lock_irq(&i915->irq_lock);
> > + i915->hotplug.short_port_mask |= BIT(dig_port->base.port);
> > + spin_unlock_irq(&i915->irq_lock);
> > +
> > + queue_work(i915->hotplug.dp_wq, &i915->hotplug.dig_port_work);
> > +}
> > +
> > /*
> > * Handle hotplug events outside the interrupt handler proper.
> > */
> > diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.h
> > b/drivers/gpu/drm/i915/display/intel_hotplug.h
> > index 777b0743257e..a704d7c94d16 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hotplug.h
> > +++ b/drivers/gpu/drm/i915/display/intel_hotplug.h
> > @@ -10,6 +10,7 @@
> >
> > struct drm_i915_private;
> > struct intel_connector;
> > +struct intel_digital_port;
> > struct intel_encoder;
> > enum port;
> >
> > @@ -18,6 +19,7 @@ enum intel_hotplug_state intel_encoder_hotplug(struct
> > intel_encoder *encoder,
> > struct intel_connector
> > *connector);
> > void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
> > u32 pin_mask, u32 long_mask);
> > +void intel_hpd_trigger_irq(struct intel_digital_port *dig_port);
> > void intel_hpd_init(struct drm_i915_private *dev_priv);
> > void intel_hpd_init_work(struct drm_i915_private *dev_priv);
> > void intel_hpd_cancel_work(struct drm_i915_private *dev_priv);
> > diff --git a/include/drm/drm_dp_mst_helper.h
> > b/include/drm/drm_dp_mst_helper.h
> > index 9e1ffcd7cb68..b230ff6f7081 100644
> > --- a/include/drm/drm_dp_mst_helper.h
> > +++ b/include/drm/drm_dp_mst_helper.h
> > @@ -475,6 +475,15 @@ struct drm_dp_mst_topology_mgr;
> > struct drm_dp_mst_topology_cbs {
> > /* create a connector for a port */
> > struct drm_connector *(*add_connector)(struct drm_dp_mst_topology_mgr
> > *mgr, struct drm_dp_mst_port *port, const char *path);
> > + /*
> > + * Checks for any pending MST interrupts, passing them to MST core for
> > + * processing, the same way an HPD IRQ pulse handler would do this.
> > + * If provided MST core calls this callback from a poll-waiting loop
> > + * when waiting for MST down message replies. The driver is expected
> > + * to guard against a race between this callback and the driver's HPD
> > + * IRQ pulse handler.
> > + */
> > + void (*poll_hpd_irq)(struct drm_dp_mst_topology_mgr *mgr);
> > };
> >
> > #define DP_MAX_PAYLOAD (sizeof(unsigned long) * 8)
> > --
> > 2.23.1
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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