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drm/uapi: Add a warning that mode flags must match the xrandr definitions 

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
This commit is contained in:
Ville Syrjälä 2016-11-03 16:10:01 +02:00 committed by Daniel Vetter
parent e587803c0a
commit 91d5ee0451
1 changed files with 9 additions and 1 deletions
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10
include/uapi/drm/drm_mode.h
View File

@ -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)