[PATCH v2 1/3] drm/probe-helper: Document drm_helper_hpd_irq_event() return value

[PATCH v2 1/3] drm/probe-helper: Document drm_helper_hpd_irq_event() return value

[Maxime Ripard]

The documentation of the drm_helper_hpd_irq_event() function didn't
document the value that function was returning. Add that part as well.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>

---

Changes from v2:
  - new patch
---
 drivers/gpu/drm/drm_probe_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 5606bca3caa8..5b77fb5c1a32 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -817,6 +817,9 @@ EXPORT_SYMBOL(drm_kms_helper_poll_fini);
  *
  * Note that a connector can be both polled and probed from the hotplug handler,
  * in case the hotplug interrupt is known to be unreliable.
+ *
+ * Returns:
+ * A boolean indicating whether the connector status changed or not
  */
 bool drm_helper_hpd_irq_event(struct drm_device *dev)
 {
-- 
2.31.1

[PATCH v2 2/3] drm/probe-helper: Create a HPD IRQ event helper for a single connector

[Maxime Ripard]

The drm_helper_hpd_irq_event() function is iterating over all the
connectors when an hotplug event is detected.

During that iteration, it will call each connector detect function and
figure out if its status changed.

Finally, if any connector changed, it will notify the user-space and the
clients that something changed on the DRM device.

This is supposed to be used for drivers that don't have a hotplug
interrupt for individual connectors. However, drivers that can use an
interrupt for a single connector are left in the dust and can either
reimplement the logic used during the iteration for each connector or
use that helper and iterate over all connectors all the time.

Since both are suboptimal, let's create a helper that will only perform
the status detection on a single connector.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>

---
Changes from v2:
  - Skip connectors with DRM_CONNECTOR_POLL_HPD in drm_helper_hpd_irq_event
  - Add drm_connector_helper_hpd_irq_event returned value documentation
  - Improve logging

Changes from v1:
  - Rename the shared function
  - Move the hotplug event notification out of the shared function
  - Added missing locks
  - Improve the documentation
  - Switched to drm_dbg_kms
---
 drivers/gpu/drm/drm_probe_helper.c | 117 +++++++++++++++++++++--------
 include/drm/drm_probe_helper.h     |   1 +
 2 files changed, 87 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 5b77fb5c1a32..a1ffc0c30b3a 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -795,6 +795,87 @@ void drm_kms_helper_poll_fini(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_kms_helper_poll_fini);
 
+static bool check_connector_changed(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	enum drm_connector_status old_status;
+	u64 old_epoch_counter;
+	bool changed = false;
+
+	/* Only handle HPD capable connectors. */
+	drm_WARN_ON(dev, !(connector->polled & DRM_CONNECTOR_POLL_HPD));
+
+	drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
+
+	old_status = connector->status;
+	old_epoch_counter = connector->epoch_counter;
+	connector->status = drm_helper_probe_detect(connector, NULL, false);
+
+	if (old_epoch_counter == connector->epoch_counter) {
+                drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Same epoch counter %llu\n",
+			    connector->base.id,
+			    connector->name,
+			    connector->epoch_counter);
+
+                return false;
+	}
+
+	drm_dbg_kms(dev, "[CONNECTOR:%d:%s] status updated from %s to %s\n",
+		    connector->base.id,
+		    connector->name,
+		    drm_get_connector_status_name(old_status)
+		    drm_get_connector_status_name(connector->status));
+
+	drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Changed epoch counter %llu => %llu\n",
+                    connector->base.id,
+                    connector->name,
+                    old_epoch_counter,
+                    connector->epoch_counter);
+
+	return true;
+}
+
+/**
+ * drm_connector_helper_hpd_irq_event - hotplug processing
+ * @connector: drm_connector
+ *
+ * Drivers can use this helper function to run a detect cycle on a connector
+ * which has the DRM_CONNECTOR_POLL_HPD flag set in its &polled member.
+ *
+ * This helper function is useful for drivers which can track hotplug
+ * interrupts for a single connector. Drivers that want to send a
+ * hotplug event for all connectors or can't track hotplug interrupts
+ * per connector need to use drm_helper_hpd_irq_event().
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ *
+ * Note that a connector can be both polled and probed from the hotplug
+ * handler, in case the hotplug interrupt is known to be unreliable.
+ *
+ * Returns:
+ * A boolean indicating whether the connector status changed or not
+ */
+bool drm_connector_helper_hpd_irq_event(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	bool changed;
+
+	mutex_lock(&dev->mode_config.mutex);
+	changed = check_connector_changed(connector);
+	mutex_unlock(&dev->mode_config.mutex);
+
+	if (changed) {
+		drm_kms_helper_hotplug_event(dev);
+		drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Sent hotplug event\n",
+			    connector->base.id,
+			    connector->name);
+	}
+
+	return changed;
+}
+EXPORT_SYMBOL(drm_connector_helper_hpd_irq_event);
+
 /**
  * drm_helper_hpd_irq_event - hotplug processing
  * @dev: drm_device
@@ -808,9 +889,10 @@ EXPORT_SYMBOL(drm_kms_helper_poll_fini);
  * interrupts for each connector.
  *
  * Drivers which support hotplug interrupts for each connector individually and
- * which have a more fine-grained detect logic should bypass this code and
- * directly call drm_kms_helper_hotplug_event() in case the connector state
- * changed.
+ * which have a more fine-grained detect logic can use
+ * drm_connector_helper_hpd_irq_event(). Alternatively, they should bypass this
+ * code and directly call drm_kms_helper_hotplug_event() in case the connector
+ * state changed.
  *
  * This function must be called from process context with no mode
  * setting locks held.
@@ -825,9 +907,7 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 {
 	struct drm_connector *connector;
 	struct drm_connector_list_iter conn_iter;
-	enum drm_connector_status old_status;
 	bool changed = false;
-	u64 old_epoch_counter;
 
 	if (!dev->mode_config.poll_enabled)
 		return false;
@@ -839,33 +919,8 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 		if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
 			continue;
 
-		old_status = connector->status;
-
-		old_epoch_counter = connector->epoch_counter;
-
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Old epoch counter %llu\n", connector->base.id,
-			      connector->name,
-			      old_epoch_counter);
-
-		connector->status = drm_helper_probe_detect(connector, NULL, false);
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
-			      connector->base.id,
-			      connector->name,
-			      drm_get_connector_status_name(old_status),
-			      drm_get_connector_status_name(connector->status));
-
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] New epoch counter %llu\n",
-			      connector->base.id,
-			      connector->name,
-			      connector->epoch_counter);
-
-		/*
-		 * Check if epoch counter had changed, meaning that we need
-		 * to send a uevent.
-		 */
-		if (old_epoch_counter != connector->epoch_counter)
+		if (check_connector_changed(connector))
 			changed = true;
-
 	}
 	drm_connector_list_iter_end(&conn_iter);
 	mutex_unlock(&dev->mode_config.mutex);
diff --git a/include/drm/drm_probe_helper.h b/include/drm/drm_probe_helper.h
index 8d3ed2834d34..04c57564c397 100644
--- a/include/drm/drm_probe_helper.h
+++ b/include/drm/drm_probe_helper.h
@@ -18,6 +18,7 @@ int drm_helper_probe_detect(struct drm_connector *connector,
 void drm_kms_helper_poll_init(struct drm_device *dev);
 void drm_kms_helper_poll_fini(struct drm_device *dev);
 bool drm_helper_hpd_irq_event(struct drm_device *dev);
+bool drm_connector_helper_hpd_irq_event(struct drm_connector *connector);
 void drm_kms_helper_hotplug_event(struct drm_device *dev);
 
 void drm_kms_helper_poll_disable(struct drm_device *dev);
-- 
2.31.1

Re: [PATCH v2 2/3] drm/probe-helper: Create a HPD IRQ event helper for a single connector

[Maxime Ripard]

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Hi Sam,

On Tue, Sep 14, 2021 at 12:41:55PM +0200, Sam Ravnborg wrote:
> On Tue, Sep 14, 2021 at 12:17:23PM +0200, Maxime Ripard wrote:
> > The drm_helper_hpd_irq_event() function is iterating over all the
> > connectors when an hotplug event is detected.
> > 
> > During that iteration, it will call each connector detect function and
> > figure out if its status changed.
> > 
> > Finally, if any connector changed, it will notify the user-space and the
> > clients that something changed on the DRM device.
> > 
> > This is supposed to be used for drivers that don't have a hotplug
> > interrupt for individual connectors. However, drivers that can use an
> > interrupt for a single connector are left in the dust and can either
> > reimplement the logic used during the iteration for each connector or
> > use that helper and iterate over all connectors all the time.
> > 
> > Since both are suboptimal, let's create a helper that will only perform
> > the status detection on a single connector.
> > 
> > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > 
> > ---
> > Changes from v2:
> >   - Skip connectors with DRM_CONNECTOR_POLL_HPD in drm_helper_hpd_irq_event
> >   - Add drm_connector_helper_hpd_irq_event returned value documentation
> >   - Improve logging
> > 
> > Changes from v1:
> >   - Rename the shared function
> >   - Move the hotplug event notification out of the shared function
> >   - Added missing locks
> >   - Improve the documentation
> >   - Switched to drm_dbg_kms
> > ---
> >  drivers/gpu/drm/drm_probe_helper.c | 117 +++++++++++++++++++++--------
> >  include/drm/drm_probe_helper.h     |   1 +
> >  2 files changed, 87 insertions(+), 31 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > index 5b77fb5c1a32..a1ffc0c30b3a 100644
> > --- a/drivers/gpu/drm/drm_probe_helper.c
> > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > @@ -795,6 +795,87 @@ void drm_kms_helper_poll_fini(struct drm_device *dev)
> >  }
> >  EXPORT_SYMBOL(drm_kms_helper_poll_fini);
> >  
> > +static bool check_connector_changed(struct drm_connector *connector)
> > +{
> > +	struct drm_device *dev = connector->dev;
> > +	enum drm_connector_status old_status;
> > +	u64 old_epoch_counter;
> > +	bool changed = false;
> > +
> > +	/* Only handle HPD capable connectors. */
> > +	drm_WARN_ON(dev, !(connector->polled & DRM_CONNECTOR_POLL_HPD));
>
> This will WARN if DRM_CONNECTOR_POLL_HPD is not set - which the previous
> code did not. I am not sure this is intentional.
> Or have I missed something?

Sorry, I misunderstood your previous comment and thought you wanted to
skip the !HPD connectors in the drm_helper_hpd_irq_event loop.

What do you think would be the proper scenario here? Just return false?

Maxime

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Re: (subset) [PATCH v2 2/3] drm/probe-helper: Create a HPD IRQ event helper for a single connector

[Maxime Ripard]

On Tue, 14 Sep 2021 12:17:23 +0200, Maxime Ripard wrote:
> The drm_helper_hpd_irq_event() function is iterating over all the
> connectors when an hotplug event is detected.
> 
> During that iteration, it will call each connector detect function and
> figure out if its status changed.
> 
> Finally, if any connector changed, it will notify the user-space and the
> clients that something changed on the DRM device.
> 
> [...]

Applied to drm/drm-misc (drm-misc-next).

Thanks!
Maxime

[PATCH v2 3/3] drm/vc4: hdmi: Actually check for the connector status in hotplug

[Maxime Ripard]

The drm_helper_hpd_irq_event() documentation states that this function
is "useful for drivers which can't or don't track hotplug interrupts for
each connector." and that "Drivers which support hotplug interrupts for
each connector individually and which have a more fine-grained detect
logic should bypass this code and directly call
drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.

However, what this actually means, and is further explained in the
drm_kms_helper_hotplug_event() documentation, is that
drm_kms_helper_hotplug_event() should be called by drivers that can
track the connection status change, and if it has changed we should call
that function.

This underlying expectation we failed to provide is that the caller of
drm_kms_helper_hotplug_event() should call drm_helper_probe_detect() to
probe the new status of the connector.

Since we didn't do it, it meant that even though we were sending the
notification to user-space and the DRM clients that something changed we
never probed or updated our internal connector status ourselves.

This went mostly unnoticed since the detect callback usually doesn't
have any side-effect. Also, if we were using the DRM fbdev emulation
(which is a DRM client), or any user-space application that can deal
with hotplug events, chances are they would react to the hotplug event
by probing the connector status eventually.

However, now that we have to enable the scrambler in detect() if it was
enabled it has a side effect, and an application such as Kodi or
modetest doesn't deal with hotplug events. This resulted with a black
screen when Kodi or modetest was running when a screen was disconnected
and then reconnected, or switched off and on.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index a3dbd1fdff7d..d9e001b9314f 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1578,10 +1578,11 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *vc4_hdmi)
 static irqreturn_t vc4_hdmi_hpd_irq_thread(int irq, void *priv)
 {
 	struct vc4_hdmi *vc4_hdmi = priv;
-	struct drm_device *dev = vc4_hdmi->connector.dev;
+	struct drm_connector *connector = &vc4_hdmi->connector;
+	struct drm_device *dev = connector->dev;
 
 	if (dev && dev->registered)
-		drm_kms_helper_hotplug_event(dev);
+		drm_connector_helper_hpd_irq_event(connector);
 
 	return IRQ_HANDLED;
 }
-- 
2.31.1

Re: [PATCH v2 3/3] drm/vc4: hdmi: Actually check for the connector status in hotplug

[Daniel Vetter]

On Tue, Sep 14, 2021 at 12:17:24PM +0200, Maxime Ripard wrote:
> The drm_helper_hpd_irq_event() documentation states that this function
> is "useful for drivers which can't or don't track hotplug interrupts for
> each connector." and that "Drivers which support hotplug interrupts for
> each connector individually and which have a more fine-grained detect
> logic should bypass this code and directly call
> drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.
> 
> However, what this actually means, and is further explained in the
> drm_kms_helper_hotplug_event() documentation, is that
> drm_kms_helper_hotplug_event() should be called by drivers that can
> track the connection status change, and if it has changed we should call
> that function.
> 
> This underlying expectation we failed to provide is that the caller of
> drm_kms_helper_hotplug_event() should call drm_helper_probe_detect() to
> probe the new status of the connector.
> 
> Since we didn't do it, it meant that even though we were sending the
> notification to user-space and the DRM clients that something changed we
> never probed or updated our internal connector status ourselves.
> 
> This went mostly unnoticed since the detect callback usually doesn't
> have any side-effect. Also, if we were using the DRM fbdev emulation
> (which is a DRM client), or any user-space application that can deal
> with hotplug events, chances are they would react to the hotplug event
> by probing the connector status eventually.
> 
> However, now that we have to enable the scrambler in detect() if it was
> enabled it has a side effect, and an application such as Kodi or
> modetest doesn't deal with hotplug events. This resulted with a black
> screen when Kodi or modetest was running when a screen was disconnected
> and then reconnected, or switched off and on.

Uh, why are you running this scrambler restore in your probe function? I
guess it works, but most drivers that do expensive hotplug restore to
handle the "no black screen for replug" use-case handle that in their own
dedicated code.

But those also tend to have per-output hpd interrupt sources, so maybe
that's why?
-Daniel

> 
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index a3dbd1fdff7d..d9e001b9314f 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -1578,10 +1578,11 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *vc4_hdmi)
>  static irqreturn_t vc4_hdmi_hpd_irq_thread(int irq, void *priv)
>  {
>  	struct vc4_hdmi *vc4_hdmi = priv;
> -	struct drm_device *dev = vc4_hdmi->connector.dev;
> +	struct drm_connector *connector = &vc4_hdmi->connector;
> +	struct drm_device *dev = connector->dev;
>  
>  	if (dev && dev->registered)
> -		drm_kms_helper_hotplug_event(dev);
> +		drm_connector_helper_hpd_irq_event(connector);
>  
>  	return IRQ_HANDLED;
>  }
> -- 
> 2.31.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH v2 3/3] drm/vc4: hdmi: Actually check for the connector status in hotplug

[Maxime Ripard]

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Hi Daniel,

On Tue, Sep 14, 2021 at 04:34:08PM +0200, Daniel Vetter wrote:
> On Tue, Sep 14, 2021 at 12:17:24PM +0200, Maxime Ripard wrote:
> > The drm_helper_hpd_irq_event() documentation states that this function
> > is "useful for drivers which can't or don't track hotplug interrupts for
> > each connector." and that "Drivers which support hotplug interrupts for
> > each connector individually and which have a more fine-grained detect
> > logic should bypass this code and directly call
> > drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.
> > 
> > However, what this actually means, and is further explained in the
> > drm_kms_helper_hotplug_event() documentation, is that
> > drm_kms_helper_hotplug_event() should be called by drivers that can
> > track the connection status change, and if it has changed we should call
> > that function.
> > 
> > This underlying expectation we failed to provide is that the caller of
> > drm_kms_helper_hotplug_event() should call drm_helper_probe_detect() to
> > probe the new status of the connector.
> > 
> > Since we didn't do it, it meant that even though we were sending the
> > notification to user-space and the DRM clients that something changed we
> > never probed or updated our internal connector status ourselves.
> > 
> > This went mostly unnoticed since the detect callback usually doesn't
> > have any side-effect. Also, if we were using the DRM fbdev emulation
> > (which is a DRM client), or any user-space application that can deal
> > with hotplug events, chances are they would react to the hotplug event
> > by probing the connector status eventually.
> > 
> > However, now that we have to enable the scrambler in detect() if it was
> > enabled it has a side effect, and an application such as Kodi or
> > modetest doesn't deal with hotplug events. This resulted with a black
> > screen when Kodi or modetest was running when a screen was disconnected
> > and then reconnected, or switched off and on.
> 
> Uh, why are you running this scrambler restore in your probe function? I
> guess it works, but most drivers that do expensive hotplug restore to
> handle the "no black screen for replug" use-case handle that in their own
> dedicated code.

That's what I got from our discussion back in June (I think?). The
discussion was about an issue we were having back then where one would
disconnect / reconnect the display while it had been setup through SCDC
to use the scrambler and higher bit ratio.

During that power cycle (that also happens when you turn a TV off and
on), the display would obviously reset its SCDC status. But if there's
nothing to handle the uevent, then the same mode remains applied
resulting in a blank screen.

If we're not supposed to set the SCDC status again in detect(), how
would we deal with this?

> But those also tend to have per-output hpd interrupt sources, so maybe
> that's why?

We do have an per-output HPD interrupt here

Maximey

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Re: (subset) [PATCH v2 3/3] drm/vc4: hdmi: Actually check for the connector status in hotplug

[Maxime Ripard]

On Tue, 14 Sep 2021 12:17:24 +0200, Maxime Ripard wrote:
> The drm_helper_hpd_irq_event() documentation states that this function
> is "useful for drivers which can't or don't track hotplug interrupts for
> each connector." and that "Drivers which support hotplug interrupts for
> each connector individually and which have a more fine-grained detect
> logic should bypass this code and directly call
> drm_kms_helper_hotplug_event()". This is thus what we ended-up doing.
> 
> [...]

Applied to drm/drm-misc (drm-misc-next).

Thanks!
Maxime

Re: (subset) [PATCH v2 1/3] drm/probe-helper: Document drm_helper_hpd_irq_event() return value

[Maxime Ripard]

On Tue, 14 Sep 2021 12:17:22 +0200, Maxime Ripard wrote:
> The documentation of the drm_helper_hpd_irq_event() function didn't
> document the value that function was returning. Add that part as well.
> 
> 

Applied to drm/drm-misc (drm-misc-next).

Thanks!
Maxime