Add some helper functions to move drm_rects between different rotated
coordinate spaces. One function does the forward transform and
another does the inverse.

Cc: dri-devel@lists.freedesktop.org
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Acked-by: NDave Airlie <airlied@linux.ie>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

Add a debug function to print the rectangle in a human readable format.

v2: Renamed drm_region to drm_rect, the function from drm_region_debug
    to drm_rect_debug_print(), and use %+d instead of +%d in the format.
v3: Use %d format for width/height in the non fixed point case as well
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: NDave Airlie <airlied@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

These functions calculate the scaling factor based on the source and
destination rectangles.

There are two version of the functions, the strict ones that will
return an error if the min/max scaling factor is exceeded, and the
relaxed versions that will adjust the src/dst rectangles in order to
keep the scaling factor withing the limits.

v2: Return error instead of adjusting regions, refactor common parts
    into one function, and split into strict and relaxed versions.
v3: Renamed drm_region to drm_rect, add "_rect_" to the function
    names.
v4: Fix "calculcate" typos
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: NDave Airlie <airlied@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

struct drm_rect represents a simple rectangle. The utility
functions are there to help driver writers.

v2: Moved the region stuff into its own file, made the smaller funcs
    static inline, used 64bit maths in the scaled clipping function to
    avoid overflows (instead it will saturate to INT_MIN or INT_MAX).
v3: Renamed drm_region to drm_rect, drm_region_clip to
    drm_rect_intersect, and drm_region_subsample to drm_rect_downscale.
v4: Renamed some function parameters, improve kernel-doc comments a bit,
    and actually generate documentation for drm_rect.[ch].
v5: s/RETUTRNS/RETURNS/
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: NDave Airlie <airlied@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>