Message-ID: <423fd809-e7a4-f13b-a379-e1efb7f4c746@xs4all.nl>
Date:   Tue, 5 Dec 2017 09:07:58 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Sean Paul <seanpaul@...omium.org>, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org
Cc:     seanpaul@...gle.com, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, daniel.vetter@...el.com
Subject: Re: [PATCH v3 3/9] drm: Add Content Protection property

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.

Regards,

	Hans

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