drm/nouveau/disp/nv50-: fix center/aspect-corrected scaling

Previously center scaling would get scaling applied to it (when it was
only supposed to center the image), and aspect-corrected scaling did not
always correctly pick whether to reduce width or height for a particular
combination of inputs/outputs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110660
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --git a/drivers/gpu/drm/nouveau/dispnv50/head.c b/drivers/gpu/drm/nouveau/dispnv50/head.c
index 48a6485ec4e0bc1dc0bb3f5d6cc076d8be700409..929d93b1677e73c3d94501c4f236201b2c556f53 100644 (file)
--- a/drivers/gpu/drm/nouveau/dispnv50/head.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/head.c
@@ -169,14 +169,34 @@ nv50_head_atomic_check_view(struct nv50_head_atom *armh,
         */
        switch (mode) {
        case DRM_MODE_SCALE_CENTER:
-               asyh->view.oW = min((u16)umode->hdisplay, asyh->view.oW);
-               asyh->view.oH = min((u16)umode_vdisplay, asyh->view.oH);
-               /* fall-through */
+               /* NOTE: This will cause scaling when the input is
+                * larger than the output.
+                */
+               asyh->view.oW = min(asyh->view.iW, asyh->view.oW);
+               asyh->view.oH = min(asyh->view.iH, asyh->view.oH);
+               break;
        case DRM_MODE_SCALE_ASPECT:
-               if (asyh->view.oH < asyh->view.oW) {
+               /* Determine whether the scaling should be on width or on
+                * height. This is done by comparing the aspect ratios of the
+                * sizes. If the output AR is larger than input AR, that means
+                * we want to change the width (letterboxed on the
+                * left/right), otherwise on the height (letterboxed on the
+                * top/bottom).
+                *
+                * E.g. 4:3 (1.333) AR image displayed on a 16:10 (1.6) AR
+                * screen will have letterboxes on the left/right. However a
+                * 16:9 (1.777) AR image on that same screen will have
+                * letterboxes on the top/bottom.
+                *
+                * inputAR = iW / iH; outputAR = oW / oH
+                * outputAR > inputAR is equivalent to oW * iH > iW * oH
+                */
+               if (asyh->view.oW * asyh->view.iH > asyh->view.iW * asyh->view.oH) {
+                       /* Recompute output width, i.e. left/right letterbox */
                        u32 r = (asyh->view.iW << 19) / asyh->view.iH;
                        asyh->view.oW = ((asyh->view.oH * r) + (r / 2)) >> 19;
                } else {
+                       /* Recompute output height, i.e. top/bottom letterbox */
                        u32 r = (asyh->view.iH << 19) / asyh->view.iW;
                        asyh->view.oH = ((asyh->view.oW * r) + (r / 2)) >> 19;
                }