From 91d5ee0451607d2a33c2b811ef3cc4a3e4578ed8 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Thu, 3 Nov 2016 16:10:01 +0200 Subject: [PATCH] drm/uapi: Add a warning that mode flags must match the xrandr definitions MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: "Lin, Jia" Cc: Akashdeep Sharma Cc: Jim Bride Cc: Jose Abreu Cc: Daniel Vetter Cc: Emil Velikov Signed-off-by: Ville Syrjälä Signed-off-by: Daniel Vetter 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 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) -- 2.20.1