Re: [RFC PATCH v2 1/9] drm: Add writeback connector type

From: Brian Starkey
Date: Wed Oct 26 2016 - 08:42:55 EST

On Wed, Oct 26, 2016 at 01:00:21PM +0200, Daniel Vetter wrote:
On Wed, Oct 26, 2016 at 09:55:00AM +0100, Brian Starkey wrote:
Writeback connectors represent writeback engines which can write the
CRTC output to a memory framebuffer. Add a writeback connector type and
related support functions.

Drivers should initialize a writeback connector with
drm_writeback_connector_init() which takes care of setting up all the
writeback-specific details on top of the normal functionality of
drm_connector_init().

Writeback connectors have a WRITEBACK_FB_ID property, used to set the
output framebuffer, PIXEL_FORMATS and PIXEL_FORMATS_SIZE used to expose
the supported writeback formats to userspace.

The drm_atomic core takes care of enforcing fairly strict semantics on
the use of writeback connectors. In short, a writeback connector can
only be included in a commit if it has both a framebuffer and a CRTC.
Conversely, you may not attach a framebuffer if the connector is not
attached to a CRTC, or if the CRTC is disabled.

When a framebuffer is attached to a writeback connector with the
WRITEBACK_FB_ID property, it is used only once (for the commit in which
it was included), and userspace can never read back the value of
WRITEBACK_FB_ID.

Changes since v1:
- Added drm_writeback.c + documentation
- Added helper to initialize writeback connector in one go
- Added core checks
- Squashed into a single commit
- Dropped the client cap
- Writeback framebuffers are no longer persistent

Signed-off-by: Brian Starkey <brian.starkey@xxxxxxx>

I think this is looking pretty good. Bunch of nitpicks below, but
otherwise I think we just need the userspace for this, plus an ack from
other people interested in this, and it's good to get merged.
-Daniel


Thanks for having another look,

---
Documentation/gpu/drm-kms.rst | 9 ++
drivers/gpu/drm/Makefile | 2 +-
drivers/gpu/drm/drm_atomic.c | 95 +++++++++++++++++++++
drivers/gpu/drm/drm_atomic_helper.c | 5 ++
drivers/gpu/drm/drm_connector.c | 4 +-
drivers/gpu/drm/drm_writeback.c | 157 +++++++++++++++++++++++++++++++++++
include/drm/drm_atomic.h | 3 +
include/drm/drm_connector.h | 12 +++
include/drm/drm_crtc.h | 20 +++++
include/drm/drm_writeback.h | 19 +++++
include/uapi/drm/drm_mode.h | 1 +
11 files changed, 325 insertions(+), 2 deletions(-)
create mode 100644 drivers/gpu/drm/drm_writeback.c
create mode 100644 include/drm/drm_writeback.h

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
index 53b872c..c3d0370 100644
--- a/Documentation/gpu/drm-kms.rst
+++ b/Documentation/gpu/drm-kms.rst
@@ -149,6 +149,15 @@ Connector Functions Reference
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
:export:

+Writeback Connectors
+--------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_writeback.c
+ :doc: overview
+
+.. kernel-doc:: drivers/gpu/drm/drm_writeback.c
+ :export:
+
Encoder Abstraction
===================

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 25c7204..2dc4a48 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -15,7 +15,7 @@ drm-y := drm_auth.o drm_bufs.o drm_cache.o \
drm_modeset_lock.o drm_atomic.o drm_bridge.o \
drm_framebuffer.o drm_connector.o drm_blend.o \
drm_encoder.o drm_mode_object.o drm_property.o \
- drm_plane.o drm_color_mgmt.o
+ drm_plane.o drm_color_mgmt.o drm_writeback.o

drm-$(CONFIG_COMPAT) += drm_ioc32.o
drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index fe37987..f434f34 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -612,6 +612,44 @@ static int drm_atomic_crtc_check(struct drm_crtc *crtc,
}

/**
+ * drm_atomic_connector_check - check connector state
+ * @connector: connector to check
+ * @state: connector state to check
+ *
+ * Provides core sanity checks for connector state.
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
+ */
+static int drm_atomic_connector_check(struct drm_connector *connector,
+ struct drm_connector_state *state)
+{
+ struct drm_crtc_state *crtc_state;
+
+ if (connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK)
+ return 0;
+
+ if (!state->fb != !state->crtc) {
+ DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] framebuffer/CRTC mismatch\n",
+ connector->base.id, connector->name);
+ return -EINVAL;
+ }
+
+ if (state->crtc)
+ crtc_state = drm_atomic_get_existing_crtc_state(state->state,
+ state->crtc);
+
+ if (state->fb && !crtc_state->active) {
+ DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] has framebuffer, but [CRTC:%d] is off\n",
+ connector->base.id, connector->name,
+ state->crtc->base.id);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+/**
* drm_atomic_get_plane_state - get plane state
* @state: global atomic state object
* @plane: plane to get state object for
@@ -1004,12 +1042,19 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
* now?) atomic writes to DPMS property:
*/
return -EINVAL;
+ } else if (property == config->writeback_fb_id_property) {
+ struct drm_framebuffer *fb = drm_framebuffer_lookup(dev, val);
+ drm_atomic_set_fb_for_connector(state, fb);
+ if (fb)
+ drm_framebuffer_unreference(fb);
} else if (connector->funcs->atomic_set_property) {
return connector->funcs->atomic_set_property(connector,
state, property, val);
} else {
return -EINVAL;
}
+
+ return 0;
}
EXPORT_SYMBOL(drm_atomic_connector_set_property);

@@ -1040,6 +1085,9 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
*val = (state->crtc) ? state->crtc->base.id : 0;
} else if (property == config->dpms_property) {
*val = connector->dpms;
+ } else if (property == config->writeback_fb_id_property) {
+ /* Writeback framebuffer is one-shot, write and forget */
+ *val = 0;
} else if (connector->funcs->atomic_get_property) {
return connector->funcs->atomic_get_property(connector,
state, property, val);
@@ -1223,6 +1271,42 @@ drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
EXPORT_SYMBOL(drm_atomic_set_crtc_for_connector);

/**
+ * drm_atomic_set_fb_for_connector - set framebuffer for (writeback) connector

Hm, I'd call this set_writeback_fb_for_connector, for even more
obviousness.


Sure.

+ * @conn_state: atomic state object for the connector
+ * @fb: fb to use for the connector
+ *
+ * This is used to set the framebuffer for a writeback connector, which outputs
+ * to a buffer instead of an actual physical connector.
+ * Changing the assigned framebuffer requires us to grab a reference to the new
+ * fb and drop the reference to the old fb, if there is one. This function
+ * takes care of all these details besides updating the pointer in the
+ * state object itself.
+ *
+ * Note: The only way conn_state can already have an fb set is if the commit
+ * sets the property more than once.
+ *
+ * See also DOC: overview in drm_writeback.c
+ */
+void
+drm_atomic_set_fb_for_connector(struct drm_connector_state *conn_state,
+ struct drm_framebuffer *fb)
+{

Should we have a WARN_ON(conn_state->connector->type != WRITEBACK here)?
Just for safety.


Yeah OK, certainly won't do any harm.

+ if (conn_state->fb)
+ drm_framebuffer_unreference(conn_state->fb);
+ if (fb)
+ drm_framebuffer_reference(fb);
+ conn_state->fb = fb;
+
+ if (fb)
+ DRM_DEBUG_ATOMIC("Set [FB:%d] for connector state %p\n",
+ fb->base.id, conn_state);
+ else
+ DRM_DEBUG_ATOMIC("Set [NOFB] for connector state %p\n",
+ conn_state);
+}
+EXPORT_SYMBOL(drm_atomic_set_fb_for_connector);
+
+/**
* drm_atomic_add_affected_connectors - add connectors for crtc
* @state: atomic state
* @crtc: DRM crtc
@@ -1376,6 +1460,8 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
struct drm_plane_state *plane_state;
struct drm_crtc *crtc;
struct drm_crtc_state *crtc_state;
+ struct drm_connector *conn;
+ struct drm_connector_state *conn_state;
int i, ret = 0;

DRM_DEBUG_ATOMIC("checking %p\n", state);
@@ -1398,6 +1484,15 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
}
}

+ for_each_connector_in_state(state, conn, conn_state, i) {
+ ret = drm_atomic_connector_check(conn, conn_state);
+ if (ret) {
+ DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] atomic core check failed\n",
+ conn->base.id, conn->name);
+ return ret;
+ }
+ }
+
if (config->funcs->atomic_check)
ret = config->funcs->atomic_check(state->dev, state);

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 2c44de3..bba8672 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3233,6 +3233,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
memcpy(state, connector->state, sizeof(*state));
if (state->crtc)
drm_connector_reference(connector);
+
+ /* Don't copy over framebuffers, they are used only once */
+ state->fb = NULL;
}
EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);

@@ -3360,6 +3363,8 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
*/
if (state->crtc)
drm_connector_unreference(state->connector);
+ if (state->fb)
+ drm_framebuffer_unreference(state->fb);
}
EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 2db7fb5..e67084d 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -86,6 +86,7 @@ static struct drm_conn_prop_enum_list drm_connector_enum_list[] = {
{ DRM_MODE_CONNECTOR_VIRTUAL, "Virtual" },
{ DRM_MODE_CONNECTOR_DSI, "DSI" },
{ DRM_MODE_CONNECTOR_DPI, "DPI" },
+ { DRM_MODE_CONNECTOR_WRITEBACK, "Writeback" },
};

void drm_connector_ida_init(void)
@@ -235,7 +236,8 @@ int drm_connector_init(struct drm_device *dev,
list_add_tail(&connector->head, &config->connector_list);
config->num_connector++;

- if (connector_type != DRM_MODE_CONNECTOR_VIRTUAL)
+ if ((connector_type != DRM_MODE_CONNECTOR_VIRTUAL) &&
+ (connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
drm_object_attach_property(&connector->base,
config->edid_property,
0);
diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
new file mode 100644
index 0000000..5a6e0ad
--- /dev/null
+++ b/drivers/gpu/drm/drm_writeback.c
@@ -0,0 +1,157 @@
+/*
+ * (C) COPYRIGHT 2016 ARM Limited. All rights reserved.
+ * Author: Brian Starkey <brian.starkey@xxxxxxx>
+ *
+ * This program is free software and is provided to you under the terms of the
+ * GNU General Public License version 2 as published by the Free Software
+ * Foundation, and any use by you of this program is subject to the terms
+ * of such GNU licence.
+ */
+
+#include <drm/drm_crtc.h>
+#include <drm/drm_property.h>
+#include <drm/drmP.h>
+
+/**
+ * DOC: overview
+ *
+ * Writeback connectors are used to expose hardware which can write the output
+ * from a CRTC to a memory buffer. They are used and act similarly to other
+ * types of connectors, with some important differences:
+ * - Writeback connectors don't provide a way to output visually to the user.
+ * - Writeback connectors should always report as "disconnected" (so that
+ * clients which don't understand them will ignore them).
+ * - Writeback connectors don't have EDID.
+ *
+ * Writeback connectors may only be attached to a CRTC when they have a
+ * framebuffer attached, and may only have a framebuffer attached when they are
+ * attached to a CRTC. The WRITEBACK_FB_ID property which sets the framebuffer
+ * applies only to a single commit (see below), which means that each and every
+ * commit which makes use of a writeback connector must set both its CRTC_ID and
+ * WRITEBACK_FB_ID. It also means that the connector's CRTC_ID must be
+ * explicitly cleared in order to make a subsequent commit which doesn't use
+ * writeback.

Hm, this is a bit an ugly fallout from our safety checks, but I guess it's
a reasonable requirement for userspace. Writeback is kinda special. Or
should we make the ->crtc pointer one-shot too? Of course only for
writeback pointers. I think that would make is simpler to use in libraries
like igt.


I sort-of agree on the ugly fallout sentiment, it took me a bit by
surprise when some of my commits started failing :-). On the userspace
side it isn't really any additional effort once you understand the
requirements though (which you learn quickly by way of -EINVAL).

I'm actually leaning towards leaving it as-is for two reasons:
1) On hardware that actually *does* need a full-modeset for writeback
routing changes, a one-shot CRTC would cause problems (need a
full-modeset every frame).
2) If there's no explicit commit to disable, we have no way to
communicate to the driver that it should disable - no-one will
ever add the connector_state to the next commit.

Both of the above *could* be handled with some special casing, but my
gut feeling is it would be tricky and a bit of a mess.

The current implementation is reasonably clean, and does seem to have
removed a few corner cases which would be likely sources of driver
bugs.

+ *
+ * Writeback connectors have several additional properties, which userspace
+ * can use to query and control them:
+ *
+ * "WRITEBACK_FB_ID":
+ * Write-only object property storing a DRM_MODE_OBJECT_FB: it stores the
+ * framebuffer to be written by the writeback connector. This property is
+ * similar to the FB_ID property on planes, but will always read as zero
+ * and is not preserved across commits.
+ * Userspace must set this property to an output buffer every time it
+ * wishes the buffer to get filled.
+ *
+ * "PIXEL_FORMATS":
+ * Immutable blob property to store the supported pixel formats table. The
+ * data is an array of u32 DRM_FORMAT_* fourcc values.
+ * Userspace can use this blob to find out what pixel formats are supported
+ * by the connector's writeback engine.
+ *
+ * "PIXEL_FORMATS_SIZE":
+ * Immutable unsigned range property storing the number of entries in the
+ * PIXEL_FORMATS array.

Blob properties already have a size, you don't need to specify it.
Gamma tables have a size since they start out with a default of NULL, so
userspace has no idea what the size should be.


OK, that makes sense. I'll drop it.

Docs are missing to clarify when the writeout is complete. Should we wait
with merging this until out fences are supported, or should we add a bit
of placeholder text here that the writeback will be completed 1 vblank
after this atomic commit was committed? I'm leaning towards including the
writeout out fences from the start.


Docs are missing because without fences I don't think it can be
defined ;-)

You think I should squash fences into this commit then? It's getting
somewhat large, but I'm not spotting any obvious places to split it
up anymore.

+ */
+
+/**
+ * create_writeback_properties - Create writeback connector-specific properties
+ * @dev: DRM device
+ *
+ * Create the properties specific to writeback connectors. These will be
+ * attached to the connector and initialised by drm_writeback_connector_init.
+ *
+ * Returns: true on success, or false if any property creation fails.
+ */

We don't do kernel-doc for non-EXPORT_SYMBOL functions, since the intended
audience is driver authors. And I think this function here is clear enough
that we don't need even a normal comment for it.


Right, I must have copied and blindly modified without thinking.

+static bool create_writeback_properties(struct drm_device *dev)
+{
+ struct drm_property *prop;
+
+ if (!dev->mode_config.writeback_fb_id_property) {
+ prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
+ "WRITEBACK_FB_ID",
+ DRM_MODE_OBJECT_FB);
+ if (!prop)
+ return false;
+ dev->mode_config.writeback_fb_id_property = prop;
+ }
+
+ if (!dev->mode_config.pixel_formats_property) {
+ prop = drm_property_create(dev, DRM_MODE_PROP_BLOB | DRM_MODE_PROP_IMMUTABLE,
+ "PIXEL_FORMATS", 0);
+ if (!prop)
+ return false;
+ dev->mode_config.pixel_formats_property = prop;
+ }
+
+ if (!dev->mode_config.pixel_formats_size_property) {
+ prop = drm_property_create_range(dev, DRM_MODE_PROP_IMMUTABLE,
+ "PIXEL_FORMATS_SIZE", 0,
+ UINT_MAX);
+ if (!prop)
+ return false;
+ dev->mode_config.pixel_formats_size_property = prop;
+ }
+
+ return true;
+}
+
+/**
+ * drm_writeback_connector_init - Initialize a writeback connector and its properties
+ * @dev: DRM device
+ * @connector: Connector to initialize
+ * @funcs: Connector funcs vtable
+ * @formats: Array of supported pixel formats for the writeback engine
+ * @n_formats: Length of the formats array
+ *
+ * This function creates the writeback-connector-specific properties if they
+ * have not been already created, initializes the connector as
+ * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
+ * values.
+ *
+ * Drivers should always use this function instead of drm_connector_init() to
+ * set up writeback connectors.
+ *
+ * Returns: 0 on success, or a negative error code
+ */
+int drm_writeback_connector_init(struct drm_device *dev,
+ struct drm_connector *connector,
+ const struct drm_connector_funcs *funcs,
+ u32 *formats, int n_formats)
+{
+ int ret;
+ struct drm_property_blob *blob;
+ struct drm_mode_config *config = &dev->mode_config;
+
+ if (!create_writeback_properties(dev))
+ return -EINVAL;
+
+ blob = drm_property_create_blob(dev, n_formats * sizeof(*formats),
+ formats);
+ if (IS_ERR(blob))
+ return PTR_ERR(blob);
+
+ ret = drm_connector_init(dev, connector, funcs,
+ DRM_MODE_CONNECTOR_WRITEBACK);
+ if (ret)
+ goto fail;
+
+ drm_object_attach_property(&connector->base,
+ config->writeback_fb_id_property, 0);
+
+ drm_object_attach_property(&connector->base,
+ config->pixel_formats_property,
+ blob->base.id);
+ connector->pixel_formats_blob_ptr = blob;
+
+ drm_object_attach_property(&connector->base,
+ config->pixel_formats_size_property,
+ n_formats);
+
+ return 0;
+
+fail:
+ drm_property_unreference_blob(blob);
+ return ret;
+}
+EXPORT_SYMBOL(drm_writeback_connector_init);
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 9701f2d..d9aff06 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -319,6 +319,9 @@ void drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
int __must_check
drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
struct drm_crtc *crtc);
+void
+drm_atomic_set_fb_for_connector(struct drm_connector_state *conn_state,
+ struct drm_framebuffer *fb);
int __must_check
drm_atomic_add_affected_connectors(struct drm_atomic_state *state,
struct drm_crtc *crtc);
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index ac9d7d8..a5e3778 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -198,6 +198,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
* @connector: backpointer to the connector
* @best_encoder: can be used by helpers and drivers to select the encoder
* @state: backpointer to global drm_atomic_state
+ * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
*/
struct drm_connector_state {
struct drm_connector *connector;
@@ -213,6 +214,8 @@ struct drm_connector_state {
struct drm_encoder *best_encoder;

struct drm_atomic_state *state;
+
+ struct drm_framebuffer *fb; /* do not write directly, use drm_atomic_set_fb_for_connector() */
};

/**
@@ -612,6 +615,15 @@ struct drm_connector {
*/
struct drm_property_blob *tile_blob_ptr;

+ /**
+ * @pixel_formats_blob_ptr:
+ *
+ * DRM blob property data for the pixel formats list on writeback
+ * connectors
+ * See also DOC: overview in drm_writeback.c

Ah, here's the link you wanted. Imo just use
drm_writeback_connector_init() instead, that's a link close enough to your
target.


OK.

+ */
+ struct drm_property_blob *pixel_formats_blob_ptr;

I'g go with a writeout prefix.

OK.

+
/* should we poll this connector for connects and disconnects */
/* hot plug detectable */
#define DRM_CONNECTOR_POLL_HPD (1 << 0)
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index fe20d8f..378baee2 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1345,6 +1345,26 @@ struct drm_mode_config {
*/
struct drm_property *suggested_y_property;

+ /**
+ * @writeback_fb_id_property: Property for writeback connectors, storing
+ * the ID of the output framebuffer.
+ * See also DOC: overview in drm_writeback.c

Same here and all of the below.

+ */
+ struct drm_property *writeback_fb_id_property;
+ /**
+ * @pixel_formats_property: Property for writeback connectors, storing
+ * an array of the supported pixel formats for the writeback engine
+ * (read-only).
+ * See also DOC: overview in drm_writeback.c
+ */
+ struct drm_property *pixel_formats_property;
+ /**
+ * @pixel_formats_size_property: Property for writeback connectors,
+ * stating the size of the pixel formats array (read-only).
+ * See also DOC: overview in drm_writeback.c
+ */
+ struct drm_property *pixel_formats_size_property;
+
/* dumb ioctl parameters */
uint32_t preferred_depth, prefer_shadow;

diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
new file mode 100644
index 0000000..afdc2742
--- /dev/null
+++ b/include/drm/drm_writeback.h
@@ -0,0 +1,19 @@
+/*
+ * (C) COPYRIGHT 2016 ARM Limited. All rights reserved.
+ * Author: Brian Starkey <brian.starkey@xxxxxxx>
+ *
+ * This program is free software and is provided to you under the terms of the
+ * GNU General Public License version 2 as published by the Free Software
+ * Foundation, and any use by you of this program is subject to the terms
+ * of such GNU licence.
+ */
+
+#ifndef __DRM_WRITEBACK_H__
+#define __DRM_WRITEBACK_H__
+
+int drm_writeback_connector_init(struct drm_device *dev,
+ struct drm_connector *connector,
+ const struct drm_connector_funcs *funcs,
+ u32 *formats, int n_formats);
+
+#endif
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index df0e350..e9cb4fe 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -247,6 +247,7 @@ struct drm_mode_get_encoder {
#define DRM_MODE_CONNECTOR_VIRTUAL 15
#define DRM_MODE_CONNECTOR_DSI 16
#define DRM_MODE_CONNECTOR_DPI 17
+#define DRM_MODE_CONNECTOR_WRITEBACK 18

struct drm_mode_get_connector {

--
1.7.9.5

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