Message-ID: <20171205152750.qcxxrzk65czqae4h@phenom.ffwll.local>
Date:   Tue, 5 Dec 2017 16:27:50 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Sean Paul <seanpaul@...omium.org>, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        daniel.vetter@...el.com, linux-kernel@...r.kernel.org,
        seanpaul@...gle.com
Subject: Re: [Intel-gfx] [PATCH v3 3/9] drm: Add Content Protection property

On Tue, Dec 05, 2017 at 09:07:58AM +0100, Hans Verkuil wrote:
> On 12/05/2017 06:15 AM, Sean Paul wrote:
> > This patch adds a new optional connector property to allow userspace to enable
> > protection over the content it is displaying. This will typically be implemented
> > by the driver using HDCP.
> > 
> > The property is a tri-state with the following values:
> > - OFF: Self explanatory, no content protection
> > - DESIRED: Userspace requests that the driver enable protection
> > - ENABLED: Once the driver has authenticated the link, it sets this value
> > 
> > The driver is responsible for downgrading ENABLED to DESIRED if the link becomes
> > unprotected. The driver should also maintain the desiredness of protection
> > across hotplug/dpms/suspend.
> > 
> > If this looks familiar, I posted [1] this 3 years ago. We have been using this
> > in ChromeOS across exynos, mediatek, and rockchip over that time.
> > 
> > Changes in v2:
> >  - Pimp kerneldoc for content_protection_property (Daniel)
> >  - Drop sysfs attribute
> > Changes in v3:
> >  - None
> > 
> > Cc: Daniel Vetter <daniel.vetter@...el.com>
> > Signed-off-by: Sean Paul <seanpaul@...omium.org>
> > 
> > [1] https://lists.freedesktop.org/archives/dri-devel/2014-December/073336.html
> > ---
> >  drivers/gpu/drm/drm_atomic.c    |  8 +++++
> >  drivers/gpu/drm/drm_connector.c | 71 +++++++++++++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/drm_sysfs.c     |  1 +
> >  include/drm/drm_connector.h     | 16 ++++++++++
> >  include/uapi/drm/drm_mode.h     |  4 +++
> >  5 files changed, 100 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index c2da5585e201..676025d755b2 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -1196,6 +1196,12 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
> >  		state->picture_aspect_ratio = val;
> >  	} else if (property == connector->scaling_mode_property) {
> >  		state->scaling_mode = val;
> > +	} else if (property == connector->content_protection_property) {
> > +		if (val == DRM_MODE_CONTENT_PROTECTION_ENABLED) {
> > +			DRM_DEBUG_KMS("only drivers can set CP Enabled\n");
> > +			return -EINVAL;
> > +		}
> > +		state->content_protection = val;
> >  	} else if (connector->funcs->atomic_set_property) {
> >  		return connector->funcs->atomic_set_property(connector,
> >  				state, property, val);
> > @@ -1275,6 +1281,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
> >  		*val = state->picture_aspect_ratio;
> >  	} else if (property == connector->scaling_mode_property) {
> >  		*val = state->scaling_mode;
> > +	} else if (property == connector->content_protection_property) {
> > +		*val = state->content_protection;
> >  	} else if (connector->funcs->atomic_get_property) {
> >  		return connector->funcs->atomic_get_property(connector,
> >  				state, property, val);
> > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > index f14b48e6e839..8626aa8f485e 100644
> > --- a/drivers/gpu/drm/drm_connector.c
> > +++ b/drivers/gpu/drm/drm_connector.c
> > @@ -698,6 +698,13 @@ static const struct drm_prop_enum_list drm_tv_subconnector_enum_list[] = {
> >  DRM_ENUM_NAME_FN(drm_get_tv_subconnector_name,
> >  		 drm_tv_subconnector_enum_list)
> >  
> > +static struct drm_prop_enum_list drm_cp_enum_list[] = {
> > +        { DRM_MODE_CONTENT_PROTECTION_OFF, "Off" },
> > +        { DRM_MODE_CONTENT_PROTECTION_DESIRED, "Desired" },
> > +        { DRM_MODE_CONTENT_PROTECTION_ENABLED, "Enabled" },
> > +};
> > +DRM_ENUM_NAME_FN(drm_get_content_protection_name, drm_cp_enum_list)
> > +
> >  /**
> >   * DOC: standard connector properties
> >   *
> > @@ -764,6 +771,34 @@ DRM_ENUM_NAME_FN(drm_get_tv_subconnector_name,
> >   *      after modeset, the kernel driver may set this to "BAD" and issue a
> >   *      hotplug uevent. Drivers should update this value using
> >   *      drm_mode_connector_set_link_status_property().
> > + * Content Protection:
> > + *	This property is used by userspace to request the kernel protect future
> > + *	content communicated over the link. When requested, kernel will apply
> > + *	the appropriate means of protection (most often HDCP), and use the
> > + *	property to tell userspace the protection is active.
> > + *
> > + *	The value of this property can be one of the following:
> > + *
> > + *	- DRM_MODE_CONTENT_PROTECTION_OFF = 0
> > + *		The link is not protected, content is transmitted in the clear.
> > + *	- DRM_MODE_CONTENT_PROTECTION_DESIRED = 1
> > + *		Userspace has requested content protection, but the link is not
> > + *		currently protected. When in this state, kernel should enable
> > + *		Content Protection as soon as possible.
> > + *	- DRM_MODE_CONTENT_PROTECTION_ENABLED = 2
> > + *		Userspace has requested content protection, and the link is
> > + *		protected. Only the driver can set the property to this value.
> > + *		If userspace attempts to set to ENABLED, kernel will return
> > + *		-EINVAL.
> > + *
> > + *	A few guidelines:
> > + *
> > + *	- DESIRED state should be preserved until userspace de-asserts it by
> > + *	  setting the property to OFF. This means ENABLED should only transition
> > + *	  to OFF when the user explicitly requests it.
> > + *	- If the state is DESIRED, kernel should attempt to re-authenticate the
> > + *	  link whenever possible. This includes across disable/enable, dpms,
> > + *	  hotplug, downstream device changes, link status failures, etc..
> >   *
> >   * Connectors also have one standardized atomic property:
> >   *
> > @@ -1047,6 +1082,42 @@ int drm_connector_attach_scaling_mode_property(struct drm_connector *connector,
> >  }
> >  EXPORT_SYMBOL(drm_connector_attach_scaling_mode_property);
> >  
> > +/**
> > + * drm_connector_attach_content_protection_property - attach content protection
> > + * property
> > + *
> > + * @connector: connector to attach CP property on.
> > + *
> > + * This is used to add support for content protection on select connectors.
> > + * Content Protection is intentionally vague to allow for different underlying
> > + * technologies, however it is most implemented by HDCP.
> > + *
> > + * The content protection will be set to &drm_connector_state.content_protection
> > + *
> > + * Returns:
> > + * Zero on success, negative errno on failure.
> > + */
> > +int drm_connector_attach_content_protection_property(
> > +		struct drm_connector *connector)
> > +{
> > +	struct drm_device *dev = connector->dev;
> > +	struct drm_property *prop;
> > +
> > +	prop = drm_property_create_enum(dev, 0, "Content Protection",
> > +					drm_cp_enum_list,
> > +					ARRAY_SIZE(drm_cp_enum_list));
> > +	if (!prop)
> > +		return -ENOMEM;
> > +
> > +	drm_object_attach_property(&connector->base, prop,
> > +				   DRM_MODE_CONTENT_PROTECTION_OFF);
> > +
> > +	connector->content_protection_property = prop;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_connector_attach_content_protection_property);
> > +
> >  /**
> >   * drm_mode_create_aspect_ratio_property - create aspect ratio property
> >   * @dev: DRM device
> > diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> > index 1c5b5ce1fd7f..2385c7e0bef5 100644
> > --- a/drivers/gpu/drm/drm_sysfs.c
> > +++ b/drivers/gpu/drm/drm_sysfs.c
> > @@ -21,6 +21,7 @@
> >  #include <drm/drm_sysfs.h>
> >  #include <drm/drmP.h>
> >  #include "drm_internal.h"
> > +#include "drm_crtc_internal.h"
> >  
> >  #define to_drm_minor(d) dev_get_drvdata(d)
> >  #define to_drm_connector(d) dev_get_drvdata(d)
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index 7a7140543012..828878addd03 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -370,6 +370,12 @@ struct drm_connector_state {
> >  	 * upscaling, mostly used for built-in panels.
> >  	 */
> >  	unsigned int scaling_mode;
> > +
> > +	/**
> > +	 * @content_protection: Connector property to request content
> > +	 * protection. This is most commonly used for HDCP.
> > +	 */
> > +	unsigned int content_protection;
> >  };
> >  
> >  /**
> > @@ -718,6 +724,7 @@ struct drm_cmdline_mode {
> >   * @tile_h_size: horizontal size of this tile.
> >   * @tile_v_size: vertical size of this tile.
> >   * @scaling_mode_property:  Optional atomic property to control the upscaling.
> > + * @content_protection_property: Optional property to control content protection
> >   *
> >   * Each connector may be connected to one or more CRTCs, or may be clonable by
> >   * another connector if they can share a CRTC.  Each connector also has a specific
> > @@ -808,6 +815,12 @@ struct drm_connector {
> >  
> >  	struct drm_property *scaling_mode_property;
> >  
> > +	/**
> > +	 * @content_protection_property: DRM ENUM property for content
> > +	 * protection
> > +	 */
> > +	struct drm_property *content_protection_property;
> > +
> >  	/**
> >  	 * @path_blob_ptr:
> >  	 *
> > @@ -1002,6 +1015,7 @@ const char *drm_get_dvi_i_subconnector_name(int val);
> >  const char *drm_get_dvi_i_select_name(int val);
> >  const char *drm_get_tv_subconnector_name(int val);
> >  const char *drm_get_tv_select_name(int val);
> > +const char *drm_get_content_protection_name(int val);
> >  
> >  int drm_mode_create_dvi_i_properties(struct drm_device *dev);
> >  int drm_mode_create_tv_properties(struct drm_device *dev,
> > @@ -1010,6 +1024,8 @@ int drm_mode_create_tv_properties(struct drm_device *dev,
> >  int drm_mode_create_scaling_mode_property(struct drm_device *dev);
> >  int drm_connector_attach_scaling_mode_property(struct drm_connector *connector,
> >  					       u32 scaling_mode_mask);
> > +int drm_connector_attach_content_protection_property(
> > +		struct drm_connector *connector);
> >  int drm_mode_create_aspect_ratio_property(struct drm_device *dev);
> >  int drm_mode_create_suggested_offset_properties(struct drm_device *dev);
> >  
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index 5597a87154e5..03f4d22305c2 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -173,6 +173,10 @@ extern "C" {
> >  		DRM_MODE_REFLECT_X | \
> >  		DRM_MODE_REFLECT_Y)
> >  
> > +/* Content Protection Flags */
> > +#define DRM_MODE_CONTENT_PROTECTION_OFF		0
> > +#define DRM_MODE_CONTENT_PROTECTION_DESIRED     1
> > +#define DRM_MODE_CONTENT_PROTECTION_ENABLED     2
> 
> What about HDCP 1.4 and HDCP 2.2? Userspace would need to know which version
> was negotiated since content protected 4k videos require HDCP 2.2. Perhaps
> provide a property with the HDCP version?
> 
> I'm also missing a method for userspace to read the BKSV from the transmitter.

Atm the only open source userspace we have is chrome os, which doesn't
care about either. That's why these two pieces have been left out, which
just need open source userspace for this stuff.

The rough idea for hdcp2 was to add a desired_type2 and enabled_type2,
which will guarantee hdcp2. _desired alone could give you either. Or we
try the most we can automatically, and publish the type1 vs. type2 stuff
in a 2nd property.

Either way, not having that from the start doesn't prevent us from adding
it later on in a backwards compatible way. Properties are rather nice this
way :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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