Re: [PATCH] drm/i915: Add hot_plug hook for hdmi encoder

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Sep 28, 2015 at 02:26:04PM +0530, Sonika Jindal wrote:
> This patch adds a separate probe function for HDMI
> EDID read over DDC channel. This function has been
> registered as a .hot_plug handler for HDMI encoder.
> 
> The current implementation of hdmi_detect()
> function re-sets the cached HDMI edid (in connector->detect_edid) in
> every detect call.This function gets called many times, sometimes
> directly from userspace probes, forcing drivers to read EDID every
> detect function call.This causes several problems like:
> 
> 1. Race conditions in multiple hot_plug / unplug cases, between
>    interrupts bottom halves and userspace detections.
> 2. Many Un-necessary EDID reads for single hotplug/unplug
> 3. HDMI complaince failures which expects only one EDID read per hotplug
> 
> This function will be serving the purpose of really reading the EDID
> by really probing the DDC channel, and updating the cached EDID.
> 
> The plan is to:
> 1. i915 IRQ handler bottom half function already calls
>    intel_encoder->hotplug() function. Adding This probe function which
>    will read the EDID only in case of a hotplug / unplug.
> 2. During init_connector this probe will be called to read the edid
> 3. Reuse the cached EDID in hdmi_detect() function.
> 
> The "< gen7" check is there because this was tested only for >=gen7
> platforms. For older platforms the hotplug/reading edid path remains same.
> 
> v2: Calling set_edid instead of hdmi_probe during init.
> Also, for platforms having DDI, intel_encoder for DP and HDMI is same
> (taken from intel_dig_port), so for DP also, hot_plug function gets called
> which is not intended here. So, check for HDMI in intel_hdmi_probe
> Rely on HPD for updating edid only for platforms gen > 8 and also for VLV.
> 
> v3: Dropping the gen < 8 || !VLV  check. Now all platforms should rely on
> hotplug or init for updating the edid.(Daniel)
> Also, calling hdmi_probe in init instead of set_edid
> 
> v4: Renaming intel_hdmi_probe to intel_hdmi_hot_plug and changing the patch
> subject. Also calling this hotplug handler from intel_hpd_init to take care
> of init resume scenarios.
> 
> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_hdmi.c    |   54 +++++++++++++++++++++++++++-------
>  drivers/gpu/drm/i915/intel_hotplug.c |   11 +++++++
>  2 files changed, 54 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> index bb33c66..9c1a308 100644
> --- a/drivers/gpu/drm/i915/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> @@ -1369,18 +1369,16 @@ intel_hdmi_set_edid(struct drm_connector *connector, bool force)
>  	return connected;
>  }
>  
> -static enum drm_connector_status
> -intel_hdmi_detect(struct drm_connector *connector, bool force)
> +void intel_hdmi_hot_plug(struct intel_encoder *intel_encoder)
>  {
> -	enum drm_connector_status status;
> -	struct intel_hdmi *intel_hdmi = intel_attached_hdmi(connector);
> -	struct drm_i915_private *dev_priv = to_i915(connector->dev);
> +	struct intel_hdmi *intel_hdmi =
> +			enc_to_intel_hdmi(&intel_encoder->base);
> +	struct intel_connector *intel_connector =
> +				intel_hdmi->attached_connector;
> +	struct drm_i915_private *dev_priv = to_i915(intel_encoder->base.dev);
>  	bool live_status = false;
>  	unsigned int retry = 3;
>  
> -	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
> -		      connector->base.id, connector->name);
> -
>  	while (!live_status && --retry) {
>  		live_status = intel_digital_port_connected(dev_priv,
>  				hdmi_to_dig_port(intel_hdmi));
> @@ -1390,15 +1388,48 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
>  	if (!live_status)
>  		DRM_DEBUG_KMS("Live status not up!");
>  
> -	intel_hdmi_unset_edid(connector);
> +	/*
> +	 * We are here, means there is a hotplug or a force
> +	 * detection. Clear the cached EDID and probe the
> +	 * DDC bus to check the current status of HDMI.
> +	 */
> +	intel_hdmi_unset_edid(&intel_connector->base);
> +	if (intel_hdmi_set_edid(&intel_connector->base, live_status))
> +		DRM_DEBUG_DRIVER("DDC probe: got EDID\n");
> +	else
> +		DRM_DEBUG_DRIVER("DDC probe: no EDID\n");
> +}
>  
> -	if (intel_hdmi_set_edid(connector, live_status)) {
> +static enum drm_connector_status
> +intel_hdmi_detect(struct drm_connector *connector, bool force)
> +{
> +	enum drm_connector_status status;
> +	struct intel_connector *intel_connector =
> +				to_intel_connector(connector);
> +
> +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
> +		      connector->base.id, connector->name);
> +
> +	/*
> +	 * There are many userspace calls which probe EDID from
> +	 * detect path. In case of multiple hotplug/unplug, these
> +	 * can cause race conditions while probing EDID. Also its
> +	 * waste of CPU cycles to read the EDID again and again
> +	 * unless there is a real hotplug.
> +	 * So, rely on hotplugs and init to read edid.
> +	 * Check connector status based on availability of cached EDID.
> +	 */
> +
> +	if (intel_connector->detect_edid) {
>  		struct intel_hdmi *intel_hdmi = intel_attached_hdmi(connector);
>  
>  		hdmi_to_dig_port(intel_hdmi)->base.type = INTEL_OUTPUT_HDMI;
>  		status = connector_status_connected;
> -	} else
> +		DRM_DEBUG_DRIVER("hdmi status = connected\n");
> +	} else {
>  		status = connector_status_disconnected;
> +		DRM_DEBUG_DRIVER("hdmi status = disconnected\n");
> +	}
>  
>  	return status;
>  }
> @@ -2131,6 +2162,7 @@ void intel_hdmi_init_connector(struct intel_digital_port *intel_dig_port,
>  	intel_connector->unregister = intel_connector_unregister;
>  
>  	intel_hdmi_add_properties(intel_hdmi, connector);
> +	intel_encoder->hot_plug = intel_hdmi_hot_plug;
>  
>  	intel_connector_attach_encoder(intel_connector, intel_encoder);
>  	drm_connector_register(connector);
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index 53c0173..36e16f6 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -459,6 +459,7 @@ void intel_hpd_init(struct drm_i915_private *dev_priv)
>  	struct drm_device *dev = dev_priv->dev;
>  	struct drm_mode_config *mode_config = &dev->mode_config;
>  	struct drm_connector *connector;
> +	struct intel_encoder *encoder;
>  	int i;
>  
>  	for_each_hpd_pin(i) {
> @@ -482,6 +483,16 @@ void intel_hpd_init(struct drm_i915_private *dev_priv)
>  	if (dev_priv->display.hpd_irq_setup)
>  		dev_priv->display.hpd_irq_setup(dev);
>  	spin_unlock_irq(&dev_priv->irq_lock);
> +
> +	/*
> +	 * Connected boot / resume scenarios can't generate new hot plug.
> +	 * So, probe it manually.
> +	 */
> +	list_for_each_entry(encoder, &dev->mode_config.encoder_list,
> +			    base.head) {
> +		if (encoder->hot_plug)
> +			encoder->hot_plug(encoder);
> +	}

Since this doesn't just change hdmi but every encoder I think we should
pull it out into a separate prep patch. Especially interactions with dp
mst handling look tricky, have you tested that nothing blows up with that?
The split-out patch should definitely explain in detail how this interacts
with dp hpd handling.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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