UPSTREAM: drm: prime: Honour O_RDWR during prime-handle-to-fd

UPSTREAM: drm: prime: Honour O_RDWR during prime-handle-to-fd

Currently DRM_IOCTL_PRIME_HANDLE_TO_FD rejects all flags except
(DRM|O)_CLOEXEC making it difficult (maybe impossible) for userspace
to mmap() the resulting dma-buf even when this is supported by the
DRM driver.

It is trivial to relax the restriction and permit read/write access.
This is safe because the flags are seldom touched by drm; mostly they
are passed verbatim to dma_buf calls.

v3 (Tiago): removed unused flags variable from drm_prime_handle_to_fd_ioctl.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1450820214-12509-2-git-send-email-tiago.vignatti@intel.com
(cherry picked from commit bfe981a0952880df43d08a050bf3ae44aaebd795)
Signed-off-by: Brian Norris <briannorris@chromium.org>
Change-Id: Ieb3c547b1a08bd9c90fe72e0a1df1757d100aa8e
Reviewed-on: https://chrome-internal-review.googlesource.com/255266
Tested-by: Brian Norris <briannorris@google.com>
Reviewed-by: Doug Anderson <dianders@google.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>