[Intel-gfx] [PATCH 2/2] drm/i915/skl: Support for 90/270 rotation

[Damien Lespiau]

On Mon, Apr 13, 2015 at 03:53:22PM +0530, Jindal, Sonika wrote:
> >>I never really got the to understand the need of reversing 90 and 270 :)
> >>The last discussion was not concluded, AFAIR.
> >>Things look correct to me and work fine with the testcase also.
> >>Is there something completely different which I am unable to get?
> >
> >BSpec gives me the impression the hw rotation is cw, whereas the drm one
> >is ccw.
> >
> Yes, HW rotation is cw as per bspec. In drm, where do we consider it as
> anti-cw? I assume it is cw because all the macros work as expected, ie cw.

The DRM is quite a direct implementation of the X semantics:

http://cgit.freedesktop.org/xorg/proto/randrproto/tree/randrproto.txt

"In Randr, the coordinate system is rotated in a counter-clockwise direction
relative to the normal orientation"

This matches the usual orientation of the trigonometric circle.

-- 
Damien