Merge tag 'topic/drm-misc-2016-11-10' of git://anongit.freedesktop.org/drm-intel into drm-next

- better atomic state debugging from Rob
- fence prep from gustavo
- sumits flushed out his backlog of pending dma-buf/fence patches from
  various people
- drm_mm leak debugging plus trying to appease Kconfig (Chris)
- a few misc things all over

* tag 'topic/drm-misc-2016-11-10' of git://anongit.freedesktop.org/drm-intel: (35 commits)
  drm: Make DRM_DEBUG_MM depend on STACKTRACE_SUPPORT
  drm/i915: Restrict DRM_DEBUG_MM automatic selection
  drm: Restrict stackdepot usage to builtin drm.ko
  drm/msm: module param to dump state on error irq
  drm/msm/mdp5: add atomic_print_state support
  drm/atomic: add debugfs file to dump out atomic state
  drm/atomic: add new drm_debug bit to dump atomic state
  drm: add helpers to go from plane state to drm_rect
  drm: add helper for printing to log or seq_file
  drm: helper macros to print composite types
  reservation: revert "wait only with non-zero timeout specified (v3)" v2
  drm/ttm: fix ttm_bo_wait
  dma-buf/fence: revert "don't wait when specified timeout is zero" (v2)
  dma-buf/fence: make timeout handling in fence_default_wait consistent (v2)
  drm/amdgpu: add the interface of waiting multiple fences (v4)
  dma-buf: return index of the first signaled fence (v2)
  MAINTAINERS: update Sync File Framework files
  dma-buf/sw_sync: put fence reference from the fence creation
  dma-buf/sw_sync: mark sync_timeline_create() static
  drm: Add stackdepot include for DRM_DEBUG_MM
  ...

11 files changed, 312 insertions, 23 deletions

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index e336e3901876..4e58137c1882 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -135,6 +135,7 @@ struct dma_buf_attachment;
 #define DRM_UT_PRIME		0x08
 #define DRM_UT_ATOMIC		0x10
 #define DRM_UT_VBL		0x20
+#define DRM_UT_STATE		0x40
 
 extern __printf(6, 7)
 void drm_dev_printk(const struct device *dev, const char *level,
@@ -306,6 +307,27 @@ void drm_printk(const char *level, unsigned int category,
 #define DRM_DEBUG_PRIME_RATELIMITED(fmt, args...)			\
 	DRM_DEV_DEBUG_PRIME_RATELIMITED(NULL, fmt, ##args)
 
+/* Format strings and argument splitters to simplify printing
+ * various "complex" objects
+ */
+#define DRM_MODE_FMT    "%d:\"%s\" %d %d %d %d %d %d %d %d %d %d 0x%x 0x%x"
+#define DRM_MODE_ARG(m) \
+	(m)->base.id, (m)->name, (m)->vrefresh, (m)->clock, \
+	(m)->hdisplay, (m)->hsync_start, (m)->hsync_end, (m)->htotal, \
+	(m)->vdisplay, (m)->vsync_start, (m)->vsync_end, (m)->vtotal, \
+	(m)->type, (m)->flags
+
+#define DRM_RECT_FMT    "%dx%d%+d%+d"
+#define DRM_RECT_ARG(r) drm_rect_width(r), drm_rect_height(r), (r)->x1, (r)->y1
+
+/* for rect's in fixed-point format: */
+#define DRM_RECT_FP_FMT "%d.%06ux%d.%06u%+d.%06u%+d.%06u"
+#define DRM_RECT_FP_ARG(r) \
+		drm_rect_width(r) >> 16, ((drm_rect_width(r) & 0xffff) * 15625) >> 10, \
+		drm_rect_height(r) >> 16, ((drm_rect_height(r) & 0xffff) * 15625) >> 10, \
+		(r)->x1 >> 16, (((r)->x1 & 0xffff) * 15625) >> 10, \
+		(r)->y1 >> 16, (((r)->y1 & 0xffff) * 15625) >> 10
+
 /*@}*/
 
 /***********************************************************************/
@@ -941,8 +963,13 @@ static inline bool drm_is_primary_client(const struct drm_file *file_priv)
 extern int drm_ioctl_permit(u32 flags, struct drm_file *file_priv);
 extern long drm_ioctl(struct file *filp,
 		      unsigned int cmd, unsigned long arg);
+#ifdef CONFIG_COMPAT
 extern long drm_compat_ioctl(struct file *filp,
 			     unsigned int cmd, unsigned long arg);
+#else
+/* Let drm_compat_ioctl be assigned to .compat_ioctl unconditionally */
+#define drm_compat_ioctl NULL
+#endif
 extern bool drm_ioctl_flags(unsigned int nr, unsigned int *flags);
 
 /* File Operations (drm_fops.c) */
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index fc8af53b18aa..331bb100b718 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -345,6 +345,8 @@ drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
 			      struct drm_crtc *crtc);
 void drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
 				 struct drm_framebuffer *fb);
+void drm_atomic_set_fence_for_plane(struct drm_plane_state *plane_state,
+				    struct dma_fence *fence);
 int __must_check
 drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
 				  struct drm_crtc *crtc);
@@ -364,6 +366,13 @@ int __must_check drm_atomic_check_only(struct drm_atomic_state *state);
 int __must_check drm_atomic_commit(struct drm_atomic_state *state);
 int __must_check drm_atomic_nonblocking_commit(struct drm_atomic_state *state);
 
+void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
+
+#ifdef CONFIG_DEBUG_FS
+struct drm_minor;
+int drm_atomic_debugfs_init(struct drm_minor *minor);
+#endif
+
 #define for_each_connector_in_state(__state, connector, connector_state, __i) \
 	for ((__i) = 0;							\
 	     (__i) < (__state)->num_connector &&				\
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index ac9d7d8e0e43..3e9727264b65 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -37,6 +37,7 @@ struct drm_crtc;
 struct drm_encoder;
 struct drm_property;
 struct drm_property_blob;
+struct drm_printer;
 struct edid;
 
 enum drm_connector_force {
@@ -481,6 +482,18 @@ struct drm_connector_funcs {
 				   const struct drm_connector_state *state,
 				   struct drm_property *property,
 				   uint64_t *val);
+
+	/**
+	 * @atomic_print_state:
+	 *
+	 * If driver subclasses struct &drm_connector_state, it should implement
+	 * this optional hook for printing additional driver specific state.
+	 *
+	 * Do not call this directly, use drm_atomic_connector_print_state()
+	 * instead.
+	 */
+	void (*atomic_print_state)(struct drm_printer *p,
+				   const struct drm_connector_state *state);
 };
 
 /* mode specified on the command line */
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index fa1aa214c8ea..8cca2a895981 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -53,6 +53,7 @@ struct drm_device;
 struct drm_mode_set;
 struct drm_file;
 struct drm_clip_rect;
+struct drm_printer;
 struct device_node;
 struct dma_fence;
 struct edid;
@@ -594,6 +595,18 @@ struct drm_crtc_funcs {
 	 */
 	int (*set_crc_source)(struct drm_crtc *crtc, const char *source,
 			      size_t *values_cnt);
+
+	/**
+	 * @atomic_print_state:
+	 *
+	 * If driver subclasses struct &drm_crtc_state, it should implement
+	 * this optional hook for printing additional driver specific state.
+	 *
+	 * Do not call this directly, use drm_atomic_crtc_print_state()
+	 * instead.
+	 */
+	void (*atomic_print_state)(struct drm_printer *p,
+				   const struct drm_crtc_state *state);
 };
 
 /**
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index 205ddcf6d55d..41ddafe92b2f 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -44,6 +44,9 @@
 #ifdef CONFIG_DEBUG_FS
 #include <linux/seq_file.h>
 #endif
+#ifdef CONFIG_DRM_DEBUG_MM
+#include <linux/stackdepot.h>
+#endif
 
 enum drm_mm_search_flags {
 	DRM_MM_SEARCH_DEFAULT =		0,
@@ -74,6 +77,9 @@ struct drm_mm_node {
 	u64 size;
 	u64 __subtree_last;
 	struct drm_mm *mm;
+#ifdef CONFIG_DRM_DEBUG_MM
+	depot_stack_handle_t stack;
+#endif
 };
 
 struct drm_mm {
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 10e449c86dbd..72478cf82147 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -361,8 +361,8 @@ struct drm_crtc_helper_funcs {
 	 *
 	 * Note that the power state of the display pipe when this function is
 	 * called depends upon the exact helpers and calling sequence the driver
-	 * has picked. See drm_atomic_commit_planes() for a discussion of the
-	 * tradeoffs and variants of plane commit helpers.
+	 * has picked. See drm_atomic_helper_commit_planes() for a discussion of
+	 * the tradeoffs and variants of plane commit helpers.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
 	 * transitional plane helpers, but it is optional.
@@ -385,8 +385,8 @@ struct drm_crtc_helper_funcs {
 	 *
 	 * Note that the power state of the display pipe when this function is
 	 * called depends upon the exact helpers and calling sequence the driver
-	 * has picked. See drm_atomic_commit_planes() for a discussion of the
-	 * tradeoffs and variants of plane commit helpers.
+	 * has picked. See drm_atomic_helper_commit_planes() for a discussion of
+	 * the tradeoffs and variants of plane commit helpers.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
 	 * transitional plane helpers, but it is optional.
@@ -940,8 +940,8 @@ struct drm_plane_helper_funcs {
 	 *
 	 * Note that the power state of the display pipe when this function is
 	 * called depends upon the exact helpers and calling sequence the driver
-	 * has picked. See drm_atomic_commit_planes() for a discussion of the
-	 * tradeoffs and variants of plane commit helpers.
+	 * has picked. See drm_atomic_helper_commit_planes() for a discussion of
+	 * the tradeoffs and variants of plane commit helpers.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
 	 * transitional plane helpers, but it is optional.
@@ -963,8 +963,8 @@ struct drm_plane_helper_funcs {
 	 *
 	 * Note that the power state of the display pipe when this function is
 	 * called depends upon the exact helpers and calling sequence the driver
-	 * has picked. See drm_atomic_commit_planes() for a discussion of the
-	 * tradeoffs and variants of plane commit helpers.
+	 * has picked. See drm_atomic_helper_commit_planes() for a discussion of
+	 * the tradeoffs and variants of plane commit helpers.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
 	 * transitional plane helpers, but it is optional.
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 0bed92c5dbd8..5b38eb94783b 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -28,15 +28,11 @@
 #include <drm/drm_mode_object.h>
 
 struct drm_crtc;
+struct drm_printer;
 
 /**
  * struct drm_plane_state - mutable plane state
  * @plane: backpointer to the plane
- * @crtc: currently bound CRTC, NULL if disabled
- * @fb: currently bound framebuffer
- * @fence: optional fence to wait for before scanning out @fb
- * @crtc_x: left position of visible portion of plane on crtc
- * @crtc_y: upper position of visible portion of plane on crtc
  * @crtc_w: width of visible portion of plane on crtc
  * @crtc_h: height of visible portion of plane on crtc
  * @src_x: left position of visible portion of plane within
@@ -57,18 +53,51 @@ struct drm_crtc;
  *	it can be trusted.
  * @src: clipped source coordinates of the plane (in 16.16)
  * @dst: clipped destination coordinates of the plane
- * @visible: visibility of the plane
  * @state: backpointer to global drm_atomic_state
  */
 struct drm_plane_state {
 	struct drm_plane *plane;
 
-	struct drm_crtc *crtc;   /* do not write directly, use drm_atomic_set_crtc_for_plane() */
-	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_plane() */
+	/**
+	 * @crtc:
+	 *
+	 * Currently bound CRTC, NULL if disabled. Do not this write directly,
+	 * use drm_atomic_set_crtc_for_plane()
+	 */
+	struct drm_crtc *crtc;
+
+	/**
+	 * @fb:
+	 *
+	 * Currently bound framebuffer. Do not write this directly, use
+	 * drm_atomic_set_fb_for_plane()
+	 */
+	struct drm_framebuffer *fb;
+
+	/**
+	 * @fence:
+	 *
+	 * Optional fence to wait for before scanning out @fb. Do not write this
+	 * directly, use drm_atomic_set_fence_for_plane()
+	 */
 	struct dma_fence *fence;
 
-	/* Signed dest location allows it to be partially off screen */
-	int32_t crtc_x, crtc_y;
+	/**
+	 * @crtc_x:
+	 *
+	 * Left position of visible portion of plane on crtc, signed dest
+	 * location allows it to be partially off screen.
+	 */
+
+	int32_t crtc_x;
+	/**
+	 * @crtc_y:
+	 *
+	 * Upper position of visible portion of plane on crtc, signed dest
+	 * location allows it to be partially off screen.
+	 */
+	int32_t crtc_y;
+
 	uint32_t crtc_w, crtc_h;
 
 	/* Source values are 16.16 fixed point */
@@ -85,15 +114,41 @@ struct drm_plane_state {
 	/* Clipped coordinates */
 	struct drm_rect src, dst;
 
-	/*
-	 * Is the plane actually visible? Can be false even
-	 * if fb!=NULL and crtc!=NULL, due to clipping.
+	/**
+	 * @visible:
+	 *
+	 * Visibility of the plane. This can be false even if fb!=NULL and
+	 * crtc!=NULL, due to clipping.
 	 */
 	bool visible;
 
 	struct drm_atomic_state *state;
 };
 
+static inline struct drm_rect
+drm_plane_state_src(const struct drm_plane_state *state)
+{
+	struct drm_rect src = {
+		.x1 = state->src_x,
+		.y1 = state->src_y,
+		.x2 = state->src_x + state->src_w,
+		.y2 = state->src_y + state->src_h,
+	};
+	return src;
+}
+
+static inline struct drm_rect
+drm_plane_state_dest(const struct drm_plane_state *state)
+{
+	struct drm_rect dest = {
+		.x1 = state->crtc_x,
+		.y1 = state->crtc_y,
+		.x2 = state->crtc_x + state->crtc_w,
+		.y2 = state->crtc_y + state->crtc_h,
+	};
+	return dest;
+}
+
 /**
  * struct drm_plane_funcs - driver plane control functions
  */
@@ -322,6 +377,18 @@ struct drm_plane_funcs {
 	 * before data structures are torndown.
 	 */
 	void (*early_unregister)(struct drm_plane *plane);
+
+	/**
+	 * @atomic_print_state:
+	 *
+	 * If driver subclasses struct &drm_plane_state, it should implement
+	 * this optional hook for printing additional driver specific state.
+	 *
+	 * Do not call this directly, use drm_atomic_plane_print_state()
+	 * instead.
+	 */
+	void (*atomic_print_state)(struct drm_printer *p,
+				   const struct drm_plane_state *state);
 };
 
 /**
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
new file mode 100644
index 000000000000..475ffe3730e9
--- /dev/null
+++ b/include/drm/drm_print.h
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2016 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * Authors:
+ * Rob Clark <robdclark@gmail.com>
+ */
+
+#ifndef DRM_PRINT_H_
+#define DRM_PRINT_H_
+
+#include <linux/seq_file.h>
+#include <linux/device.h>
+
+/**
+ * DOC: print
+ *
+ * A simple wrapper for dev_printk(), seq_printf(), etc.  Allows same
+ * debug code to be used for both debugfs and printk logging.
+ *
+ * For example::
+ *
+ *     void log_some_info(struct drm_printer *p)
+ *     {
+ *             drm_printf(p, "foo=%d\n", foo);
+ *             drm_printf(p, "bar=%d\n", bar);
+ *     }
+ *
+ *     #ifdef CONFIG_DEBUG_FS
+ *     void debugfs_show(struct seq_file *f)
+ *     {
+ *             struct drm_printer p = drm_seq_file_printer(f);
+ *             log_some_info(&p);
+ *     }
+ *     #endif
+ *
+ *     void some_other_function(...)
+ *     {
+ *             struct drm_printer p = drm_info_printer(drm->dev);
+ *             log_some_info(&p);
+ *     }
+ */
+
+/**
+ * struct drm_printer - drm output "stream"
+ * @printfn: actual output fxn
+ * @arg: output fxn specific data
+ *
+ * Do not use struct members directly.  Use drm_printer_seq_file(),
+ * drm_printer_info(), etc to initialize.  And drm_printf() for output.
+ */
+struct drm_printer {
+	void (*printfn)(struct drm_printer *p, struct va_format *vaf);
+	void *arg;
+};
+
+void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
+
+/**
+ * drm_printf - print to a &drm_printer stream
+ * @p: the &drm_printer
+ * @f: format string
+ */
+void drm_printf(struct drm_printer *p, const char *f, ...);
+
+
+/**
+ * drm_seq_file_printer - construct a &drm_printer that outputs to &seq_file
+ * @f:  the struct &seq_file to output to
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_seq_file_printer(struct seq_file *f)
+{
+	struct drm_printer p = {
+		.printfn = __drm_printfn_seq_file,
+		.arg = f,
+	};
+	return p;
+}
+
+/**
+ * drm_info_printer - construct a &drm_printer that outputs to dev_printk()
+ * @dev: the struct &device pointer
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_info_printer(struct device *dev)
+{
+	struct drm_printer p = {
+		.printfn = __drm_printfn_info,
+		.arg = dev,
+	};
+	return p;
+}
+
+#endif /* DRM_PRINT_H_ */
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index ba60c043a5d3..fcf4b1971eba 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -382,7 +382,8 @@ signed long dma_fence_wait_timeout(struct dma_fence *,
 				   bool intr, signed long timeout);
 signed long dma_fence_wait_any_timeout(struct dma_fence **fences,
 				       uint32_t count,
-				       bool intr, signed long timeout);
+				       bool intr, signed long timeout,
+				       uint32_t *idx);
 
 /**
  * dma_fence_wait - sleep until the fence gets signaled
diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
index 4684f378f046..2191a9e4f3db 100644
--- a/include/uapi/drm/amdgpu_drm.h
+++ b/include/uapi/drm/amdgpu_drm.h
@@ -50,6 +50,7 @@ extern "C" {
 #define DRM_AMDGPU_WAIT_CS		0x09
 #define DRM_AMDGPU_GEM_OP		0x10
 #define DRM_AMDGPU_GEM_USERPTR		0x11
+#define DRM_AMDGPU_WAIT_FENCES		0x12
 
 #define DRM_IOCTL_AMDGPU_GEM_CREATE	DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_CREATE, union drm_amdgpu_gem_create)
 #define DRM_IOCTL_AMDGPU_GEM_MMAP	DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_MMAP, union drm_amdgpu_gem_mmap)
@@ -63,6 +64,7 @@ extern "C" {
 #define DRM_IOCTL_AMDGPU_WAIT_CS	DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_WAIT_CS, union drm_amdgpu_wait_cs)
 #define DRM_IOCTL_AMDGPU_GEM_OP		DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_OP, struct drm_amdgpu_gem_op)
 #define DRM_IOCTL_AMDGPU_GEM_USERPTR	DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_USERPTR, struct drm_amdgpu_gem_userptr)
+#define DRM_IOCTL_AMDGPU_WAIT_FENCES	DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_WAIT_FENCES, union drm_amdgpu_wait_fences)
 
 #define AMDGPU_GEM_DOMAIN_CPU		0x1
 #define AMDGPU_GEM_DOMAIN_GTT		0x2
@@ -307,6 +309,32 @@ union drm_amdgpu_wait_cs {
 	struct drm_amdgpu_wait_cs_out out;
 };
 
+struct drm_amdgpu_fence {
+	__u32 ctx_id;
+	__u32 ip_type;
+	__u32 ip_instance;
+	__u32 ring;
+	__u64 seq_no;
+};
+
+struct drm_amdgpu_wait_fences_in {
+	/** This points to uint64_t * which points to fences */
+	__u64 fences;
+	__u32 fence_count;
+	__u32 wait_all;
+	__u64 timeout_ns;
+};
+
+struct drm_amdgpu_wait_fences_out {
+	__u32 status;
+	__u32 first_signaled;
+};
+
+union drm_amdgpu_wait_fences {
+	struct drm_amdgpu_wait_fences_in in;
+	struct drm_amdgpu_wait_fences_out out;
+};
+
 #define AMDGPU_GEM_OP_GET_GEM_CREATE_INFO	0
 #define AMDGPU_GEM_OP_SET_PLACEMENT		1
 
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 084b50a02dc5..01000c9f7c2c 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -47,7 +47,15 @@ extern "C" {
 #define DRM_MODE_TYPE_DRIVER	(1<<6)
 
 /* Video mode flags */
-/* bit compatible with the xorg definitions. */
+/* bit compatible with the xrandr RR_ definitions (bits 0-13)
+ *
+ * ABI warning: Existing userspace really expects
+ * the mode flags to match the xrandr definitions. Any
+ * changes that don't match the xrandr definitions will
+ * likely need a new client cap or some other mechanism
+ * to avoid breaking existing userspace. This includes
+ * allocating new flags in the previously unused bits!
+ */
 #define DRM_MODE_FLAG_PHSYNC			(1<<0)
 #define DRM_MODE_FLAG_NHSYNC			(1<<1)
 #define DRM_MODE_FLAG_PVSYNC			(1<<2)