[PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

For old-school component TV and CRT connectors, we require a heavyweight
load-detection mechanism. This involves setting up a CRTC and sending a
signal to the output, before reading back any response. As that is quite
slow and CPU heavy, the process is only performed when the output
detection is forced by user request. As it requires a driving CRTC, we
often don't have the resources to complete the probe. This leaves us in
a quandary where the unforced path just returns the old connector
status, but the forced detection path elects to return UNKNOWN. If we
have an active connection, we likely have the resources available to
complete the probe - but if it is currently disconnected, then it
becomes unknown and triggers a hotplug event, with often quite unfortunate
userspace behaviour (e.g. one output is blanked and the spurious TV
turned on).

To reduce spurious hotplug events on older devices, we can prevent
transitions between disconnected <-> unknown.

References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_crt.c | 39 ++++++++++++++++++---------------------
 drivers/gpu/drm/i915/intel_tv.c  | 25 +++++++++----------------
 2 files changed, 27 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 521af2c..70c5288 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -666,8 +666,6 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 	struct intel_encoder *intel_encoder = &crt->base;
 	enum intel_display_power_domain power_domain;
 	enum drm_connector_status status;
-	struct intel_load_detect_pipe tmp;
-	struct drm_modeset_acquire_ctx ctx;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
@@ -703,27 +701,26 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 		goto out;
 	}
 
-	if (!force) {
-		status = connector->status;
-		goto out;
-	}
-
-	drm_modeset_acquire_init(&ctx, 0);
-
-	/* for pre-945g platforms use load detect */
-	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
-		if (intel_crt_detect_ddc(connector))
-			status = connector_status_connected;
-		else if (INTEL_INFO(dev)->gen < 4)
-			status = intel_crt_load_detect(crt);
-		else
+	status = connector->status;
+	if (force) {
+		struct intel_load_detect_pipe tmp;
+		struct drm_modeset_acquire_ctx ctx;
+
+		drm_modeset_acquire_init(&ctx, 0);
+
+		/* for pre-945g platforms use load detect */
+		if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
+			if (intel_crt_detect_ddc(connector))
+				status = connector_status_connected;
+			else if (INTEL_INFO(dev)->gen < 4)
+				status = intel_crt_load_detect(crt);
+			intel_release_load_detect_pipe(connector, &tmp, &ctx);
+		} else if (status == connector_status_connected)
 			status = connector_status_unknown;
-		intel_release_load_detect_pipe(connector, &tmp, &ctx);
-	} else
-		status = connector_status_unknown;
 
-	drm_modeset_drop_locks(&ctx);
-	drm_modeset_acquire_fini(&ctx);
+		drm_modeset_drop_locks(&ctx);
+		drm_modeset_acquire_fini(&ctx);
+	}
 
 out:
 	intel_display_power_put(dev_priv, power_domain);
diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index 8b9d325..e3c0fed 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1313,44 +1313,37 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
 static enum drm_connector_status
 intel_tv_detect(struct drm_connector *connector, bool force)
 {
-	struct drm_display_mode mode;
 	struct intel_tv *intel_tv = intel_attached_tv(connector);
-	enum drm_connector_status status;
-	int type;
+	enum drm_connector_status status = connector->status;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
 		      force);
-
-	mode = reported_modes[0];
-
 	if (force) {
+		struct drm_display_mode mode = reported_modes[0];
 		struct intel_load_detect_pipe tmp;
 		struct drm_modeset_acquire_ctx ctx;
 
 		drm_modeset_acquire_init(&ctx, 0);
 
 		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
-			type = intel_tv_detect_type(intel_tv, connector);
+			int type = intel_tv_detect_type(intel_tv, connector);
 			intel_release_load_detect_pipe(connector, &tmp, &ctx);
 			status = type < 0 ?
 				connector_status_disconnected :
 				connector_status_connected;
-		} else
+			intel_tv->type = type;
+		} else if (status == connector_status_connected)
 			status = connector_status_unknown;
 
 		drm_modeset_drop_locks(&ctx);
 		drm_modeset_acquire_fini(&ctx);
-	} else
-		return connector->status;
 
-	if (status != connector_status_connected)
-		return status;
-
-	intel_tv->type = type;
-	intel_tv_find_better_format(connector);
+		if (status == connector_status_connected)
+			intel_tv_find_better_format(connector);
+	}
 
-	return connector_status_connected;
+	return status;
 }
 
 static const struct input_res {
-- 
1.9.1

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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Ville Syrjälä]

On Thu, Jun 04, 2015 at 04:26:18PM +0100, Chris Wilson wrote:
> For old-school component TV and CRT connectors, we require a heavyweight
> load-detection mechanism. This involves setting up a CRTC and sending a
> signal to the output, before reading back any response. As that is quite
> slow and CPU heavy, the process is only performed when the output
> detection is forced by user request. As it requires a driving CRTC, we
> often don't have the resources to complete the probe. This leaves us in
> a quandary where the unforced path just returns the old connector
> status, but the forced detection path elects to return UNKNOWN. If we
> have an active connection, we likely have the resources available to
> complete the probe - but if it is currently disconnected, then it
> becomes unknown and triggers a hotplug event, with often quite unfortunate
> userspace behaviour (e.g. one output is blanked and the spurious TV
> turned on).
> 
> To reduce spurious hotplug events on older devices, we can prevent
> transitions between disconnected <-> unknown.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_crt.c | 39 ++++++++++++++++++---------------------
>  drivers/gpu/drm/i915/intel_tv.c  | 25 +++++++++----------------
>  2 files changed, 27 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
> index 521af2c..70c5288 100644
> --- a/drivers/gpu/drm/i915/intel_crt.c
> +++ b/drivers/gpu/drm/i915/intel_crt.c
> @@ -666,8 +666,6 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  	struct intel_encoder *intel_encoder = &crt->base;
>  	enum intel_display_power_domain power_domain;
>  	enum drm_connector_status status;
> -	struct intel_load_detect_pipe tmp;
> -	struct drm_modeset_acquire_ctx ctx;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
> @@ -703,27 +701,26 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  		goto out;
>  	}
>  
> -	if (!force) {
> -		status = connector->status;
> -		goto out;
> -	}
> -
> -	drm_modeset_acquire_init(&ctx, 0);
> -
> -	/* for pre-945g platforms use load detect */
> -	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
> -		if (intel_crt_detect_ddc(connector))
> -			status = connector_status_connected;
> -		else if (INTEL_INFO(dev)->gen < 4)
> -			status = intel_crt_load_detect(crt);
> -		else
> +	status = connector->status;
> +	if (force) {
> +		struct intel_load_detect_pipe tmp;
> +		struct drm_modeset_acquire_ctx ctx;
> +
> +		drm_modeset_acquire_init(&ctx, 0);
> +
> +		/* for pre-945g platforms use load detect */
> +		if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
> +			if (intel_crt_detect_ddc(connector))
> +				status = connector_status_connected;

Hmm. I wonder what this DDC detection is doing here in the first place.
It doesn't need a load detect pipe, and if we end up here we've already
tried and failed at DDC based detection earlier.

> +			else if (INTEL_INFO(dev)->gen < 4)
> +				status = intel_crt_load_detect(crt);
> +			intel_release_load_detect_pipe(connector, &tmp, &ctx);
> +		} else if (status == connector_status_connected)
>  			status = connector_status_unknown;
> -		intel_release_load_detect_pipe(connector, &tmp, &ctx);
> -	} else
> -		status = connector_status_unknown;
>  
> -	drm_modeset_drop_locks(&ctx);
> -	drm_modeset_acquire_fini(&ctx);
> +		drm_modeset_drop_locks(&ctx);
> +		drm_modeset_acquire_fini(&ctx);
> +	}

The main bit there seems to be the
'else if (status == connector_status_connected)' check. The rest is
mostly indentation changes, but this does pull the load detect
variables into the same block, so perhaps it's better this way.

The logic makes sense to me. If it was disconnected and we don't have
free pipes to figure out if it might be connected now, just leave it
as disconnected instead of changing to unknown.

>  
>  out:
>  	intel_display_power_put(dev_priv, power_domain);
> diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
> index 8b9d325..e3c0fed 100644
> --- a/drivers/gpu/drm/i915/intel_tv.c
> +++ b/drivers/gpu/drm/i915/intel_tv.c
> @@ -1313,44 +1313,37 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
>  static enum drm_connector_status
>  intel_tv_detect(struct drm_connector *connector, bool force)
>  {
> -	struct drm_display_mode mode;
>  	struct intel_tv *intel_tv = intel_attached_tv(connector);
> -	enum drm_connector_status status;
> -	int type;
> +	enum drm_connector_status status = connector->status;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
>  		      force);
> -
> -	mode = reported_modes[0];
> -
>  	if (force) {
> +		struct drm_display_mode mode = reported_modes[0];
>  		struct intel_load_detect_pipe tmp;
>  		struct drm_modeset_acquire_ctx ctx;
>  
>  		drm_modeset_acquire_init(&ctx, 0);
>  
>  		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
> -			type = intel_tv_detect_type(intel_tv, connector);
> +			int type = intel_tv_detect_type(intel_tv, connector);
>  			intel_release_load_detect_pipe(connector, &tmp, &ctx);
>  			status = type < 0 ?
>  				connector_status_disconnected :
>  				connector_status_connected;
> -		} else
> +			intel_tv->type = type;
> +		} else if (status == connector_status_connected)
>  			status = connector_status_unknown;
>  
>  		drm_modeset_drop_locks(&ctx);
>  		drm_modeset_acquire_fini(&ctx);
> -	} else
> -		return connector->status;
>  
> -	if (status != connector_status_connected)
> -		return status;
> -
> -	intel_tv->type = type;
> -	intel_tv_find_better_format(connector);
> +		if (status == connector_status_connected)
> +			intel_tv_find_better_format(connector);
> +	}

So besides avoiding the disconnected->unknown transition, the other thing
we now seem to do is set intel_tv->type to -1 when we find that things
are disconnected. However that doesn't seem to be user visible, and I
can't see any place in the code where it should cause problems.

It is a bit inconsistent however due to the fact that we initialize type
to DRM_MODE_CONNECTOR_Unknown, and later we use the -1 to indicate more
or less the same thing. Seems like we should pick or the other for
consistency.

Apart from the little things like the weird pre-exising extra
ddc detect and the intel_tv->type inconsistency this patch looks OK to
me, so
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  
> -	return connector_status_connected;
> +	return status;
>  }
>  
>  static const struct input_res {
> -- 
> 1.9.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

On Thu, Jun 04, 2015 at 07:28:31PM +0300, Ville Syrjälä wrote:
> So besides avoiding the disconnected->unknown transition, the other thing
> we now seem to do is set intel_tv->type to -1 when we find that things
> are disconnected. However that doesn't seem to be user visible, and I
> can't see any place in the code where it should cause problems.

Mostly because after the first refactor, it was not immediately obvious
that doing intel_tv->type = type would be valid, so I only wanted to set
intel_tv->type when doing load_detect. Fortunately, the value is only
used when connected - but it could conceivable be used when the
connector status is UNKNOWN but then it is either still set as
DRM_MODE_CONNECTOR_Unknown from init, or the last known active value.

> It is a bit inconsistent however due to the fact that we initialize type
> to DRM_MODE_CONNECTOR_Unknown, and later we use the -1 to indicate more
> or less the same thing. Seems like we should pick or the other for
> consistency.

Yup. Might as well do that now, or else it will another few years before
the next pass through tumbleweed town.
 
> Apart from the little things like the weird pre-exising extra
> ddc detect and the intel_tv->type inconsistency this patch looks OK to
> me, so
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

That DDC is definitely weird, but one I'm not inclined to touch without
good reason.  Preparing a v2 with the minor tv_type change, I'll
presumptively stick your r-b on it ;)
-chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

For old-school component TV and CRT connectors, we require a heavyweight
load-detection mechanism. This involves setting up a CRTC and sending a
signal to the output, before reading back any response. As that is quite
slow and CPU heavy, the process is only performed when the output
detection is forced by user request. As it requires a driving CRTC, we
often don't have the resources to complete the probe. This leaves us in
a quandary where the unforced path just returns the old connector
status, but the forced detection path elects to return UNKNOWN. If we
have an active connection, we likely have the resources available to
complete the probe - but if it is currently disconnected, then it
becomes unknown and triggers a hotplug event, with often quite unfortunate
userspace behaviour (e.g. one output is blanked and the spurious TV
turned on).

To reduce spurious hotplug events on older devices, we can prevent
transitions between disconnected <-> unknown.

v2: Convert tv_type to use proper unknown enum (Ville)

References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
---
 drivers/gpu/drm/i915/intel_crt.c | 39 ++++++++++++++++++---------------------
 drivers/gpu/drm/i915/intel_tv.c  | 37 ++++++++++++++-----------------------
 2 files changed, 32 insertions(+), 44 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 521af2c..70c5288 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -666,8 +666,6 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 	struct intel_encoder *intel_encoder = &crt->base;
 	enum intel_display_power_domain power_domain;
 	enum drm_connector_status status;
-	struct intel_load_detect_pipe tmp;
-	struct drm_modeset_acquire_ctx ctx;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
@@ -703,27 +701,26 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 		goto out;
 	}
 
-	if (!force) {
-		status = connector->status;
-		goto out;
-	}
-
-	drm_modeset_acquire_init(&ctx, 0);
-
-	/* for pre-945g platforms use load detect */
-	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
-		if (intel_crt_detect_ddc(connector))
-			status = connector_status_connected;
-		else if (INTEL_INFO(dev)->gen < 4)
-			status = intel_crt_load_detect(crt);
-		else
+	status = connector->status;
+	if (force) {
+		struct intel_load_detect_pipe tmp;
+		struct drm_modeset_acquire_ctx ctx;
+
+		drm_modeset_acquire_init(&ctx, 0);
+
+		/* for pre-945g platforms use load detect */
+		if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
+			if (intel_crt_detect_ddc(connector))
+				status = connector_status_connected;
+			else if (INTEL_INFO(dev)->gen < 4)
+				status = intel_crt_load_detect(crt);
+			intel_release_load_detect_pipe(connector, &tmp, &ctx);
+		} else if (status == connector_status_connected)
 			status = connector_status_unknown;
-		intel_release_load_detect_pipe(connector, &tmp, &ctx);
-	} else
-		status = connector_status_unknown;
 
-	drm_modeset_drop_locks(&ctx);
-	drm_modeset_acquire_fini(&ctx);
+		drm_modeset_drop_locks(&ctx);
+		drm_modeset_acquire_fini(&ctx);
+	}
 
 out:
 	intel_display_power_put(dev_priv, power_domain);
diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index 8b9d325..135584f 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1233,7 +1233,6 @@ intel_tv_detect_type(struct intel_tv *intel_tv,
 	intel_wait_for_vblank(intel_tv->base.base.dev,
 			      to_intel_crtc(intel_tv->base.base.crtc)->pipe);
 
-	type = -1;
 	tv_dac = I915_READ(TV_DAC);
 	DRM_DEBUG_KMS("TV detected: %x, %x\n", tv_ctl, tv_dac);
 	/*
@@ -1253,7 +1252,7 @@ intel_tv_detect_type(struct intel_tv *intel_tv,
 		type = DRM_MODE_CONNECTOR_Component;
 	} else {
 		DRM_DEBUG_KMS("Unrecognised TV connection\n");
-		type = -1;
+		type = DRM_MODE_CONNECTOR_Unknown;
 	}
 
 	I915_WRITE(TV_DAC, save_tv_dac & ~TVDAC_STATE_CHG_EN);
@@ -1313,44 +1312,36 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
 static enum drm_connector_status
 intel_tv_detect(struct drm_connector *connector, bool force)
 {
-	struct drm_display_mode mode;
-	struct intel_tv *intel_tv = intel_attached_tv(connector);
-	enum drm_connector_status status;
-	int type;
+	enum drm_connector_status status = connector->status;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
 		      connector->base.id, connector->name,
 		      force);
-
-	mode = reported_modes[0];
-
 	if (force) {
+		struct intel_tv *intel_tv = intel_attached_tv(connector);
+		struct drm_display_mode mode = reported_modes[0];
 		struct intel_load_detect_pipe tmp;
 		struct drm_modeset_acquire_ctx ctx;
 
 		drm_modeset_acquire_init(&ctx, 0);
 
 		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
-			type = intel_tv_detect_type(intel_tv, connector);
+			intel_tv->type =
+				intel_tv_detect_type(intel_tv, connector);
 			intel_release_load_detect_pipe(connector, &tmp, &ctx);
-			status = type < 0 ?
-				connector_status_disconnected :
-				connector_status_connected;
-		} else
+			if (intel_tv->type != DRM_MODE_CONNECTOR_Unknown) {
+				intel_tv_find_better_format(connector);
+				status = connector_status_connected;
+			} else
+				status = connector_status_disconnected;
+		} else if (status == connector_status_connected)
 			status = connector_status_unknown;
 
 		drm_modeset_drop_locks(&ctx);
 		drm_modeset_acquire_fini(&ctx);
-	} else
-		return connector->status;
-
-	if (status != connector_status_connected)
-		return status;
-
-	intel_tv->type = type;
-	intel_tv_find_better_format(connector);
+	}
 
-	return connector_status_connected;
+	return status;
 }
 
 static const struct input_res {
-- 
1.9.1

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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6536
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  270/270              270/270
ILK                                  303/303              303/303
SNB                                  312/312              312/312
IVB                                  343/343              343/343
BYT                                  287/287              287/287
BDW                                  318/318              318/318
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6544
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -1              270/270              269/270
ILK                                  303/303              303/303
SNB                                  312/312              312/312
IVB                                  343/343              343/343
BYT                                  287/287              287/287
BDW                                  318/318              318/318
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*PNV  igt@gem_tiled_pread_pwrite      PASS(1)      FAIL(1)
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Daniel Vetter]

On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> For old-school component TV and CRT connectors, we require a heavyweight
> load-detection mechanism. This involves setting up a CRTC and sending a
> signal to the output, before reading back any response. As that is quite
> slow and CPU heavy, the process is only performed when the output
> detection is forced by user request. As it requires a driving CRTC, we
> often don't have the resources to complete the probe. This leaves us in
> a quandary where the unforced path just returns the old connector
> status, but the forced detection path elects to return UNKNOWN. If we
> have an active connection, we likely have the resources available to
> complete the probe - but if it is currently disconnected, then it
> becomes unknown and triggers a hotplug event, with often quite unfortunate
> userspace behaviour (e.g. one output is blanked and the spurious TV
> turned on).
> 
> To reduce spurious hotplug events on older devices, we can prevent
> transitions between disconnected <-> unknown.
> 
> v2: Convert tv_type to use proper unknown enum (Ville)
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]

This solution is at odds with

commit b7703726251191cd9f3ef3a80b2d9667901eec95
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Jan 21 08:45:22 2015 +0100

    drm/probe-helper: clamp unknown connector status in the poll work

We're missing this bit of logic from the hotplug handlers, but that was
somewhat intentional since a hotplug should indicate that something has
changed. And in the i915 hpd handler we filter by source.

Given that the report is older than me having resurrect that patch can we
close it as fixed or do I miss something?

Thanks, Daniel

> ---
>  drivers/gpu/drm/i915/intel_crt.c | 39 ++++++++++++++++++---------------------
>  drivers/gpu/drm/i915/intel_tv.c  | 37 ++++++++++++++-----------------------
>  2 files changed, 32 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
> index 521af2c..70c5288 100644
> --- a/drivers/gpu/drm/i915/intel_crt.c
> +++ b/drivers/gpu/drm/i915/intel_crt.c
> @@ -666,8 +666,6 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  	struct intel_encoder *intel_encoder = &crt->base;
>  	enum intel_display_power_domain power_domain;
>  	enum drm_connector_status status;
> -	struct intel_load_detect_pipe tmp;
> -	struct drm_modeset_acquire_ctx ctx;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
> @@ -703,27 +701,26 @@ intel_crt_detect(struct drm_connector *connector, bool force)
>  		goto out;
>  	}
>  
> -	if (!force) {
> -		status = connector->status;
> -		goto out;
> -	}
> -
> -	drm_modeset_acquire_init(&ctx, 0);
> -
> -	/* for pre-945g platforms use load detect */
> -	if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
> -		if (intel_crt_detect_ddc(connector))
> -			status = connector_status_connected;
> -		else if (INTEL_INFO(dev)->gen < 4)
> -			status = intel_crt_load_detect(crt);
> -		else
> +	status = connector->status;
> +	if (force) {
> +		struct intel_load_detect_pipe tmp;
> +		struct drm_modeset_acquire_ctx ctx;
> +
> +		drm_modeset_acquire_init(&ctx, 0);
> +
> +		/* for pre-945g platforms use load detect */
> +		if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
> +			if (intel_crt_detect_ddc(connector))
> +				status = connector_status_connected;
> +			else if (INTEL_INFO(dev)->gen < 4)
> +				status = intel_crt_load_detect(crt);
> +			intel_release_load_detect_pipe(connector, &tmp, &ctx);
> +		} else if (status == connector_status_connected)
>  			status = connector_status_unknown;
> -		intel_release_load_detect_pipe(connector, &tmp, &ctx);
> -	} else
> -		status = connector_status_unknown;
>  
> -	drm_modeset_drop_locks(&ctx);
> -	drm_modeset_acquire_fini(&ctx);
> +		drm_modeset_drop_locks(&ctx);
> +		drm_modeset_acquire_fini(&ctx);
> +	}
>  
>  out:
>  	intel_display_power_put(dev_priv, power_domain);
> diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
> index 8b9d325..135584f 100644
> --- a/drivers/gpu/drm/i915/intel_tv.c
> +++ b/drivers/gpu/drm/i915/intel_tv.c
> @@ -1233,7 +1233,6 @@ intel_tv_detect_type(struct intel_tv *intel_tv,
>  	intel_wait_for_vblank(intel_tv->base.base.dev,
>  			      to_intel_crtc(intel_tv->base.base.crtc)->pipe);
>  
> -	type = -1;
>  	tv_dac = I915_READ(TV_DAC);
>  	DRM_DEBUG_KMS("TV detected: %x, %x\n", tv_ctl, tv_dac);
>  	/*
> @@ -1253,7 +1252,7 @@ intel_tv_detect_type(struct intel_tv *intel_tv,
>  		type = DRM_MODE_CONNECTOR_Component;
>  	} else {
>  		DRM_DEBUG_KMS("Unrecognised TV connection\n");
> -		type = -1;
> +		type = DRM_MODE_CONNECTOR_Unknown;
>  	}
>  
>  	I915_WRITE(TV_DAC, save_tv_dac & ~TVDAC_STATE_CHG_EN);
> @@ -1313,44 +1312,36 @@ static void intel_tv_find_better_format(struct drm_connector *connector)
>  static enum drm_connector_status
>  intel_tv_detect(struct drm_connector *connector, bool force)
>  {
> -	struct drm_display_mode mode;
> -	struct intel_tv *intel_tv = intel_attached_tv(connector);
> -	enum drm_connector_status status;
> -	int type;
> +	enum drm_connector_status status = connector->status;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] force=%d\n",
>  		      connector->base.id, connector->name,
>  		      force);
> -
> -	mode = reported_modes[0];
> -
>  	if (force) {
> +		struct intel_tv *intel_tv = intel_attached_tv(connector);
> +		struct drm_display_mode mode = reported_modes[0];
>  		struct intel_load_detect_pipe tmp;
>  		struct drm_modeset_acquire_ctx ctx;
>  
>  		drm_modeset_acquire_init(&ctx, 0);
>  
>  		if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
> -			type = intel_tv_detect_type(intel_tv, connector);
> +			intel_tv->type =
> +				intel_tv_detect_type(intel_tv, connector);
>  			intel_release_load_detect_pipe(connector, &tmp, &ctx);
> -			status = type < 0 ?
> -				connector_status_disconnected :
> -				connector_status_connected;
> -		} else
> +			if (intel_tv->type != DRM_MODE_CONNECTOR_Unknown) {
> +				intel_tv_find_better_format(connector);
> +				status = connector_status_connected;
> +			} else
> +				status = connector_status_disconnected;
> +		} else if (status == connector_status_connected)
>  			status = connector_status_unknown;
>  
>  		drm_modeset_drop_locks(&ctx);
>  		drm_modeset_acquire_fini(&ctx);
> -	} else
> -		return connector->status;
> -
> -	if (status != connector_status_connected)
> -		return status;
> -
> -	intel_tv->type = type;
> -	intel_tv_find_better_format(connector);
> +	}
>  
> -	return connector_status_connected;
> +	return status;
>  }
>  
>  static const struct input_res {
> -- 
> 1.9.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > For old-school component TV and CRT connectors, we require a heavyweight
> > load-detection mechanism. This involves setting up a CRTC and sending a
> > signal to the output, before reading back any response. As that is quite
> > slow and CPU heavy, the process is only performed when the output
> > detection is forced by user request. As it requires a driving CRTC, we
> > often don't have the resources to complete the probe. This leaves us in
> > a quandary where the unforced path just returns the old connector
> > status, but the forced detection path elects to return UNKNOWN. If we
> > have an active connection, we likely have the resources available to
> > complete the probe - but if it is currently disconnected, then it
> > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > userspace behaviour (e.g. one output is blanked and the spurious TV
> > turned on).
> > 
> > To reduce spurious hotplug events on older devices, we can prevent
> > transitions between disconnected <-> unknown.
> > 
> > v2: Convert tv_type to use proper unknown enum (Ville)
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> 
> This solution is at odds with
> 
> commit b7703726251191cd9f3ef3a80b2d9667901eec95
> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> Date:   Wed Jan 21 08:45:22 2015 +0100
> 
>     drm/probe-helper: clamp unknown connector status in the poll work
> 
> We're missing this bit of logic from the hotplug handlers, but that was
> somewhat intentional since a hotplug should indicate that something has
> changed. And in the i915 hpd handler we filter by source.
> 
> Given that the report is older than me having resurrect that patch can we
> close it as fixed or do I miss something?

It's a different path. This also concerns the actual forced reprobe
fluctuating between two states.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Daniel Vetter]

On Mon, Jun 15, 2015 at 01:35:21PM +0100, Chris Wilson wrote:
> On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> > On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > > For old-school component TV and CRT connectors, we require a heavyweight
> > > load-detection mechanism. This involves setting up a CRTC and sending a
> > > signal to the output, before reading back any response. As that is quite
> > > slow and CPU heavy, the process is only performed when the output
> > > detection is forced by user request. As it requires a driving CRTC, we
> > > often don't have the resources to complete the probe. This leaves us in
> > > a quandary where the unforced path just returns the old connector
> > > status, but the forced detection path elects to return UNKNOWN. If we
> > > have an active connection, we likely have the resources available to
> > > complete the probe - but if it is currently disconnected, then it
> > > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > > userspace behaviour (e.g. one output is blanked and the spurious TV
> > > turned on).
> > > 
> > > To reduce spurious hotplug events on older devices, we can prevent
> > > transitions between disconnected <-> unknown.
> > > 
> > > v2: Convert tv_type to use proper unknown enum (Ville)
> > > 
> > > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > 
> > This solution is at odds with
> > 
> > commit b7703726251191cd9f3ef3a80b2d9667901eec95
> > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Date:   Wed Jan 21 08:45:22 2015 +0100
> > 
> >     drm/probe-helper: clamp unknown connector status in the poll work
> > 
> > We're missing this bit of logic from the hotplug handlers, but that was
> > somewhat intentional since a hotplug should indicate that something has
> > changed. And in the i915 hpd handler we filter by source.
> > 
> > Given that the report is older than me having resurrect that patch can we
> > close it as fixed or do I miss something?
> 
> It's a different path. This also concerns the actual forced reprobe
> fluctuating between two states.

In that case I still think it should be in the probe helpers. Which raises
the policy decision whether we should ever hand unkown back to userspace
since apparently it just can't cope sensible with it. But that call should
be done consistently accross drivers.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

On Mon, Jun 15, 2015 at 03:03:39PM +0200, Daniel Vetter wrote:
> On Mon, Jun 15, 2015 at 01:35:21PM +0100, Chris Wilson wrote:
> > On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> > > On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > > > For old-school component TV and CRT connectors, we require a heavyweight
> > > > load-detection mechanism. This involves setting up a CRTC and sending a
> > > > signal to the output, before reading back any response. As that is quite
> > > > slow and CPU heavy, the process is only performed when the output
> > > > detection is forced by user request. As it requires a driving CRTC, we
> > > > often don't have the resources to complete the probe. This leaves us in
> > > > a quandary where the unforced path just returns the old connector
> > > > status, but the forced detection path elects to return UNKNOWN. If we
> > > > have an active connection, we likely have the resources available to
> > > > complete the probe - but if it is currently disconnected, then it
> > > > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > > > userspace behaviour (e.g. one output is blanked and the spurious TV
> > > > turned on).
> > > > 
> > > > To reduce spurious hotplug events on older devices, we can prevent
> > > > transitions between disconnected <-> unknown.
> > > > 
> > > > v2: Convert tv_type to use proper unknown enum (Ville)
> > > > 
> > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > 
> > > This solution is at odds with
> > > 
> > > commit b7703726251191cd9f3ef3a80b2d9667901eec95
> > > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Date:   Wed Jan 21 08:45:22 2015 +0100
> > > 
> > >     drm/probe-helper: clamp unknown connector status in the poll work
> > > 
> > > We're missing this bit of logic from the hotplug handlers, but that was
> > > somewhat intentional since a hotplug should indicate that something has
> > > changed. And in the i915 hpd handler we filter by source.
> > > 
> > > Given that the report is older than me having resurrect that patch can we
> > > close it as fixed or do I miss something?
> > 
> > It's a different path. This also concerns the actual forced reprobe
> > fluctuating between two states.
> 
> In that case I still think it should be in the probe helpers. Which raises
> the policy decision whether we should ever hand unkown back to userspace
> since apparently it just can't cope sensible with it. But that call should
> be done consistently accross drivers.

Hmm, the probe helper is not the central arbiter here which is a problem
in moving it entirely into its domain. UNKNOWN makes a sense form the hw
perspective, and we still need to report that status before any probes
are made at all (whether that is init/resume) and the problem in this
case is not so much as userspace mishandling it, but the fluctuation
between UNKNOWN/DISCONNECTED is causing activity and reconfiguration not
entirely of its own fault.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Daniel Vetter]

On Mon, Jun 15, 2015 at 02:37:58PM +0100, Chris Wilson wrote:
> On Mon, Jun 15, 2015 at 03:03:39PM +0200, Daniel Vetter wrote:
> > On Mon, Jun 15, 2015 at 01:35:21PM +0100, Chris Wilson wrote:
> > > On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> > > > On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > > > > For old-school component TV and CRT connectors, we require a heavyweight
> > > > > load-detection mechanism. This involves setting up a CRTC and sending a
> > > > > signal to the output, before reading back any response. As that is quite
> > > > > slow and CPU heavy, the process is only performed when the output
> > > > > detection is forced by user request. As it requires a driving CRTC, we
> > > > > often don't have the resources to complete the probe. This leaves us in
> > > > > a quandary where the unforced path just returns the old connector
> > > > > status, but the forced detection path elects to return UNKNOWN. If we
> > > > > have an active connection, we likely have the resources available to
> > > > > complete the probe - but if it is currently disconnected, then it
> > > > > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > > > > userspace behaviour (e.g. one output is blanked and the spurious TV
> > > > > turned on).
> > > > > 
> > > > > To reduce spurious hotplug events on older devices, we can prevent
> > > > > transitions between disconnected <-> unknown.
> > > > > 
> > > > > v2: Convert tv_type to use proper unknown enum (Ville)
> > > > > 
> > > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > > 
> > > > This solution is at odds with
> > > > 
> > > > commit b7703726251191cd9f3ef3a80b2d9667901eec95
> > > > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > Date:   Wed Jan 21 08:45:22 2015 +0100
> > > > 
> > > >     drm/probe-helper: clamp unknown connector status in the poll work
> > > > 
> > > > We're missing this bit of logic from the hotplug handlers, but that was
> > > > somewhat intentional since a hotplug should indicate that something has
> > > > changed. And in the i915 hpd handler we filter by source.
> > > > 
> > > > Given that the report is older than me having resurrect that patch can we
> > > > close it as fixed or do I miss something?
> > > 
> > > It's a different path. This also concerns the actual forced reprobe
> > > fluctuating between two states.
> > 
> > In that case I still think it should be in the probe helpers. Which raises
> > the policy decision whether we should ever hand unkown back to userspace
> > since apparently it just can't cope sensible with it. But that call should
> > be done consistently accross drivers.
> 
> Hmm, the probe helper is not the central arbiter here which is a problem
> in moving it entirely into its domain. UNKNOWN makes a sense form the hw
> perspective, and we still need to report that status before any probes
> are made at all (whether that is init/resume) and the problem in this
> case is not so much as userspace mishandling it, but the fluctuation
> between UNKNOWN/DISCONNECTED is causing activity and reconfiguration not
> entirely of its own fault.

Well for the poll worker part of the probe helpers I went with

	if (new_status == unknown)
		connector->status = old_status;

which takes care of the init/resume time unknown->(dis)connected
transition correctly while filtering the noise. Adding that to the
synchronous users probe function (which is the only one that sets force ==
true) would achieve what you want I think. But it also means that we
almost always filter out unknown and never let userspace known that the hw
detection is uncertain.

Maybe we instead need a drm helper module option to clamp unknown
uncondiotionally to disconnected to allow users to hack around silly
userspace?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
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http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

On Mon, Jun 15, 2015 at 05:18:40PM +0200, Daniel Vetter wrote:
> On Mon, Jun 15, 2015 at 02:37:58PM +0100, Chris Wilson wrote:
> > On Mon, Jun 15, 2015 at 03:03:39PM +0200, Daniel Vetter wrote:
> > > On Mon, Jun 15, 2015 at 01:35:21PM +0100, Chris Wilson wrote:
> > > > On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> > > > > On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > > > > > For old-school component TV and CRT connectors, we require a heavyweight
> > > > > > load-detection mechanism. This involves setting up a CRTC and sending a
> > > > > > signal to the output, before reading back any response. As that is quite
> > > > > > slow and CPU heavy, the process is only performed when the output
> > > > > > detection is forced by user request. As it requires a driving CRTC, we
> > > > > > often don't have the resources to complete the probe. This leaves us in
> > > > > > a quandary where the unforced path just returns the old connector
> > > > > > status, but the forced detection path elects to return UNKNOWN. If we
> > > > > > have an active connection, we likely have the resources available to
> > > > > > complete the probe - but if it is currently disconnected, then it
> > > > > > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > > > > > userspace behaviour (e.g. one output is blanked and the spurious TV
> > > > > > turned on).
> > > > > > 
> > > > > > To reduce spurious hotplug events on older devices, we can prevent
> > > > > > transitions between disconnected <-> unknown.
> > > > > > 
> > > > > > v2: Convert tv_type to use proper unknown enum (Ville)
> > > > > > 
> > > > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > > > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > > > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v1]
> > > > > 
> > > > > This solution is at odds with
> > > > > 
> > > > > commit b7703726251191cd9f3ef3a80b2d9667901eec95
> > > > > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > > Date:   Wed Jan 21 08:45:22 2015 +0100
> > > > > 
> > > > >     drm/probe-helper: clamp unknown connector status in the poll work
> > > > > 
> > > > > We're missing this bit of logic from the hotplug handlers, but that was
> > > > > somewhat intentional since a hotplug should indicate that something has
> > > > > changed. And in the i915 hpd handler we filter by source.
> > > > > 
> > > > > Given that the report is older than me having resurrect that patch can we
> > > > > close it as fixed or do I miss something?
> > > > 
> > > > It's a different path. This also concerns the actual forced reprobe
> > > > fluctuating between two states.
> > > 
> > > In that case I still think it should be in the probe helpers. Which raises
> > > the policy decision whether we should ever hand unkown back to userspace
> > > since apparently it just can't cope sensible with it. But that call should
> > > be done consistently accross drivers.
> > 
> > Hmm, the probe helper is not the central arbiter here which is a problem
> > in moving it entirely into its domain. UNKNOWN makes a sense form the hw
> > perspective, and we still need to report that status before any probes
> > are made at all (whether that is init/resume) and the problem in this
> > case is not so much as userspace mishandling it, but the fluctuation
> > between UNKNOWN/DISCONNECTED is causing activity and reconfiguration not
> > entirely of its own fault.
> 
> Well for the poll worker part of the probe helpers I went with
> 
> 	if (new_status == unknown)
> 		connector->status = old_status;
> 
> which takes care of the init/resume time unknown->(dis)connected
> transition correctly while filtering the noise. Adding that to the
> synchronous users probe function (which is the only one that sets force ==
> true) would achieve what you want I think. But it also means that we
> almost always filter out unknown and never let userspace known that the hw
> detection is uncertain.

I thought that connected->unknown was less likely and of more
significance than disconnected<->unknown. But that was from thinking
that the output was in use whilst it was connected, and so should always
have the resources available to do the detection. On second thought, we
should always just suppress the ->unknown transition.

The best way to then report the unreliable detection would to be report
an error trying to connect to the CRT/TV (by a vblank load detect cycle)
and signal EREMOTEIO in enable -- but the modesetting code still does
not report errors, despite their continued prevalence (such as training
failures).

> Maybe we instead need a drm helper module option to clamp unknown
> uncondiotionally to disconnected to allow users to hack around silly
> userspace?

We have userspace that respects unknown, after it is what the fb_helper
was copied from. Unknown is unknown, userspace can either treat it as
potentially connector or potentially disconnected depending on best that
suites its purposes. So I don't think a global change is sensible.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Daniel Vetter]

On Fri, Jun 19, 2015 at 02:21:59PM +0100, Chris Wilson wrote:
> > Maybe we instead need a drm helper module option to clamp unknown
> > uncondiotionally to disconnected to allow users to hack around silly
> > userspace?
> 
> We have userspace that respects unknown, after it is what the fb_helper
> was copied from. Unknown is unknown, userspace can either treat it as
> potentially connector or potentially disconnected depending on best that
> suites its purposes. So I don't think a global change is sensible.

Well you implement some kind of clamping in i915 drivers. My stance is
that no matter what exact kind of clamping we agree on it should be
implemented in shared code in the probe helpers. And we already have quite
a bit of unknown duct-taping going on in the probe helpers, but it seems
to not be enough. And tbh I'm not sure what more we need short of just
clamping unknown in general.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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