From 91d5ee0451607d2a33c2b811ef3cc4a3e4578ed8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Thu, 3 Nov 2016 16:10:01 +0200
Subject: [PATCH] drm/uapi: Add a warning that mode flags must match the xrandr
definitions
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Existing userspace expected the mode flags to match the xrandr
definitions 1:1, and even adding new flags in he previously unused
bits is likely to break existing userspace. Add a comment warning
people about this potential trap.
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: "Lin, Jia" <lin.a.jia@intel.com>
Cc: Akashdeep Sharma <akashdeep.sharma@intel.com>
Cc: Jim Bride <jim.bride@linux.intel.com>
Cc: Jose Abreu <Jose.Abreu@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1478182201-26086-1-git-send-email-ville.syrjala@linux.intel.com
---
include/uapi/drm/drm_mode.h | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 084b50a02dc5f..01000c9f7c2cf 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)
--
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