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Subject[PATCH 5.2 39/45] drm/nouveau/disp/nv50-: fix center/aspect-corrected scaling
Date
From: Ilia Mirkin <imirkin@alum.mit.edu>

[ Upstream commit 533f4752407543f488a9118d817b8c504352b6fb ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/nouveau/dispnv50/head.c | 28 +++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/head.c b/drivers/gpu/drm/nouveau/dispnv50/head.c
index 06ee23823a689..acfafc4bda0e1 100644
--- 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;
}
--
2.20.1


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