[Intel-gfx] [PATCH v6 3/4] drm/i915/display: add hotplug.suspended flag
Imre Deak
imre.deak at intel.com
Thu Aug 25 14:57:27 UTC 2022
On Thu, Aug 25, 2022 at 01:24:04PM +0200, Andrzej Hajda wrote:
> On 24.08.2022 13:22, Imre Deak wrote:
> > On Tue, Aug 23, 2022 at 11:48:01PM +0200, Andrzej Hajda wrote:
> > >
> > >
> > > On 22.08.2022 19:27, Imre Deak wrote:
> > > > On Fri, Jul 22, 2022 at 02:51:42PM +0200, Andrzej Hajda wrote:
> > > > > HPD events during driver removal can be generated by hardware and
> > > > > software frameworks - drm_dp_mst, the former we can avoid by disabling
> > > > > interrupts, the latter can be triggered by any drm_dp_mst transaction,
> > > > > and this is too late. Introducing suspended flag allows to solve this
> > > > > chicken-egg problem.
> > > > intel_hpd_cancel_work() is always called after suspending MST and
> > > > disabling IRQs (with the order I suggested in patch 1). If both of these
> > > > have disabled the corresponding functionality (MST, IRQs) properly with
> > > > all their MST/IRQ scheduled works guaranteed to not get rescheduled,
> > > > then it's not clear how could either intel_hpd_trigger_irq() or an IRQ
> > > > work run. So the problematic sequence would need a better explanation.
> > >
> > > I am not familiar with MST but as I understand from earlier discussion MST
> > > framework can be called during driver removal code even after
> > > intel_dp_mst_suspend.
> >
> > Not sure how that happens, but it looks wrong. One way I can imagine is
> > that connector detection re-enables MST, which should be prevented then.
>
> I am not MST expert and atm I have no access to the machine on which I could
> look for real prove.
> As I understand intel_dp_mst_suspend prevents only downstream devices to
> initiate transactions, it does not prevent transactions initiated from i915
> driver.
> My guesses for such transactions are:
> - any ioctl/sysfs/drm_property access initiated by user which can involve
> MST tranaction (set brightness, read EDID, reading capabilities, statuses,
> ....), unless they are already blocked, how?
In theory all these should be blocked already, after
i915_driver_unregister() has returned; for the above cases in particular
via drm_connector_unregister_all().
> - maybe some mode_config disabling code (for example intel_mst_disable_dp) -
This should be called already via i915_driver_unregister() ->
intel_display_driver_unregister() -> drm_atomic_helper_shutdown().
> intel_mode_config_cleanup is called after intel_dp_mst_suspend.
This should only free the allocated objects etc, but not do any
transactions.
> And since MST transfer can timeout it can trigger
> drm_dp_mst_wait_tx_reply --> mgr->cbs->poll_hpd_irq(mgr) -->
> intel_dp_mst_poll_hpd_irq --> intel_hpd_trigger_irq.
>
> If such situation happens after intel_dp_mst_suspend
> i915->hotplug.dig_port_work will be queued, and we have risk of
> use-after-free.
>
> If this analysis looks incorrect I can send patches 1, 2, 4 with your
> comments addressed. CI probably will verify this anyway.
Ok. I suppose blocking detection based on a new flag would mean avoiding
scheduling and flushing hotplug.hotplug_work already as the first step
in intel_display_driver_unregister() and somewhere early during system
suspend.
> Regards
> Andrzej
>
>
> >
> > > And since MST transfer can timeout it can trigger
> > > drm_dp_mst_wait_tx_reply --> mgr->cbs->poll_hpd_irq(mgr) -->
> > > intel_dp_mst_poll_hpd_irq --> intel_hpd_trigger_irq.
> > >
> > > So actually this patch supersedes the 1st patch.
> > >
> > > >
> > > > There's also already
> > > > dev_priv->runtime_pm.irqs_enabled
> > > > showing if hotplug interrupts are disabled (along with all other IRQs).
> > >
> > > So it is slightly different, this patch introduces flag indicating if HPD is
> > > enabled, we can have IRQs not related to HPD, and HPD events not related to
> > > IRQs.
> >
> > In its current form I can't see a difference. What would make sense is
> > to add a flag that prevents connector detection (which would
> > incorrectly enable MST for instace), but leave the handling of other
> > interrupts enabled. That flag would be set already before suspending
> > MST.
> >
> > > Regards
> > > Andrzej
> > >
> > > >
> > > > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5950
> > > > > Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
> > > > > Reviewed-by: Arun R Murthy <arun.r.murthy at intel.com>
> > > > > ---
> > > > > drivers/gpu/drm/i915/display/intel_display.c | 2 +-
> > > > > drivers/gpu/drm/i915/display/intel_hotplug.c | 11 ++++++++++-
> > > > > drivers/gpu/drm/i915/display/intel_hotplug.h | 2 +-
> > > > > drivers/gpu/drm/i915/i915_driver.c | 4 ++--
> > > > > drivers/gpu/drm/i915/i915_drv.h | 2 ++
> > > > > 5 files changed, 16 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > > > > index f1c765ac7ab8aa..cd6139bb36151b 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > > > > @@ -9022,7 +9022,7 @@ void intel_modeset_driver_remove_noirq(struct drm_i915_private *i915)
> > > > > intel_dp_mst_suspend(i915);
> > > > > /* MST is the last user of HPD work */
> > > > > - intel_hpd_cancel_work(i915);
> > > > > + intel_hpd_suspend(i915);
> > > > > /* poll work can call into fbdev, hence clean that up afterwards */
> > > > > intel_fbdev_fini(i915);
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c b/drivers/gpu/drm/i915/display/intel_hotplug.c
> > > > > index 5f8b4f481cff9a..e1d384cb99df6b 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_hotplug.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
> > > > > @@ -303,6 +303,8 @@ static void i915_digport_work_func(struct work_struct *work)
> > > > > u32 old_bits = 0;
> > > > > spin_lock_irq(&dev_priv->irq_lock);
> > > > > + if (dev_priv->hotplug.suspended)
> > > > > + return spin_unlock_irq(&dev_priv->irq_lock);
> > > > > long_port_mask = dev_priv->hotplug.long_port_mask;
> > > > > dev_priv->hotplug.long_port_mask = 0;
> > > > > short_port_mask = dev_priv->hotplug.short_port_mask;
> > > > > @@ -353,6 +355,8 @@ 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);
> > > > > + if (i915->hotplug.suspended)
> > > > > + return spin_unlock_irq(&i915->irq_lock);
> > > > > i915->hotplug.short_port_mask |= BIT(dig_port->base.port);
> > > > > spin_unlock_irq(&i915->irq_lock);
> > > > > @@ -475,6 +479,9 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
> > > > > spin_lock(&dev_priv->irq_lock);
> > > > > + if (dev_priv->hotplug.suspended)
> > > > > + return spin_unlock(&dev_priv->irq_lock);
> > > > > +
> > > > > /*
> > > > > * Determine whether ->hpd_pulse() exists for each pin, and
> > > > > * whether we have a short or a long pulse. This is needed
> > > > > @@ -603,6 +610,7 @@ void intel_hpd_init(struct drm_i915_private *dev_priv)
> > > > > * just to make the assert_spin_locked checks happy.
> > > > > */
> > > > > spin_lock_irq(&dev_priv->irq_lock);
> > > > > + dev_priv->hotplug.suspended = false;
> > > > > intel_hpd_irq_setup(dev_priv);
> > > > > spin_unlock_irq(&dev_priv->irq_lock);
> > > > > }
> > > > > @@ -721,13 +729,14 @@ void intel_hpd_init_work(struct drm_i915_private *dev_priv)
> > > > > intel_hpd_irq_storm_reenable_work);
> > > > > }
> > > > > -void intel_hpd_cancel_work(struct drm_i915_private *dev_priv)
> > > > > +void intel_hpd_suspend(struct drm_i915_private *dev_priv)
> > > > > {
> > > > > if (!HAS_DISPLAY(dev_priv))
> > > > > return;
> > > > > spin_lock_irq(&dev_priv->irq_lock);
> > > > > + dev_priv->hotplug.suspended = true;
> > > > > dev_priv->hotplug.long_port_mask = 0;
> > > > > dev_priv->hotplug.short_port_mask = 0;
> > > > > dev_priv->hotplug.event_bits = 0;
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.h b/drivers/gpu/drm/i915/display/intel_hotplug.h
> > > > > index b87e95d606e668..54bddc4dd63421 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_hotplug.h
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_hotplug.h
> > > > > @@ -23,7 +23,7 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
> > > > > 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);
> > > > > +void intel_hpd_suspend(struct drm_i915_private *dev_priv);
> > > > > enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
> > > > > enum port port);
> > > > > bool intel_hpd_disable(struct drm_i915_private *dev_priv, enum hpd_pin pin);
> > > > > diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
> > > > > index deb8a8b76965a1..57a063a306e3a4 100644
> > > > > --- a/drivers/gpu/drm/i915/i915_driver.c
> > > > > +++ b/drivers/gpu/drm/i915/i915_driver.c
> > > > > @@ -1092,7 +1092,7 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
> > > > > intel_dp_mst_suspend(i915);
> > > > > intel_runtime_pm_disable_interrupts(i915);
> > > > > - intel_hpd_cancel_work(i915);
> > > > > + intel_hpd_suspend(i915);
> > > > > intel_suspend_encoders(i915);
> > > > > intel_shutdown_encoders(i915);
> > > > > @@ -1161,7 +1161,7 @@ static int i915_drm_suspend(struct drm_device *dev)
> > > > > intel_dp_mst_suspend(dev_priv);
> > > > > intel_runtime_pm_disable_interrupts(dev_priv);
> > > > > - intel_hpd_cancel_work(dev_priv);
> > > > > + intel_hpd_suspend(dev_priv);
> > > > > intel_suspend_encoders(dev_priv);
> > > > > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > > > > index d25647be25d18b..dc1562b95d7ade 100644
> > > > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > > > @@ -106,6 +106,8 @@ struct vlv_s0ix_state;
> > > > > #define HPD_STORM_DEFAULT_THRESHOLD 50
> > > > > struct i915_hotplug {
> > > > > + bool suspended;
> > > > > +
> > > > > struct delayed_work hotplug_work;
> > > > > const u32 *hpd, *pch_hpd;
> > > > > --
> > > > > 2.25.1
> > > > >
> > >
>
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