drm/i915: handle shared framebuffers when flipping

drm/i915: handle shared framebuffers when flipping

commit be9a3dbf65a69933b06011f049b1e2fdfa6bc8b9 upstream.

If a framebuffer is shared across CRTCs, the x,y position of one of them
is likely to be something other than the origin (e.g. for extended
desktop configs).  So calculate the offset at flip time so such
configurations can work.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=28518.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Thomas M. <tmezzadra@gmail.com>
Tested-by: fangxun <xunx.fang@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>