[PATCH v2] drm/nouveau/kms/nve4-nv108: Don't advertise 256x256 cursor support yet

[Lyude Paul <lyude@redhat.com>]

While Kepler does technically support 256x256 cursors, it turns out that
in order for us to use these correctly we need to make sure that the cursor
plane uses a ctxdma that is set to use small (4K)/large (128K) pages -
whichever is applicable to the given cursor surface.

Right now however, we share the main kmsVramCtxDma that is used for all but
the ovly plane which defaults to small pages - resulting in artifacts when
we use 256x256 cursor surfaces. So until we teach nouveau to use a separate
ctxdma for the cursor, let's just stop advertising 256x256 cursors by
default - which should fix the issues that users were seeing.

Coincidentally - this is also why small ovlys don't work on Kepler: the
ctxdma we use for ovlys is set to large pages.

Changes since v2:
* Fix comments and patch description

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: d3b2f0f7921c ("drm/nouveau/kms/nv50-: Report max cursor size to userspace")
Cc: <stable@vger.kernel.org> # v5.11+
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 196612addfd6..d92cf9e17ac3 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -2693,9 +2693,19 @@ nv50_display_create(struct drm_device *dev)
 	else
 		nouveau_display(dev)->format_modifiers = disp50xx_modifiers;
 
-	if (disp->disp->object.oclass >= GK104_DISP) {
+	/* FIXME: 256x256 cursors are supported on Kepler, however unlike Maxwell and later
+	 * generations Kepler requires that we specify the page type, small (4K) or large (128K),
+	 * correctly for the ctxdma being used on curs/ovly. We currently share a ctxdma across all
+	 * display planes (except ovly) that defaults to small pages, which results in artifacting
+	 * on 256x256 cursors. Until we teach nouveau to create an appropriate ctxdma for the cursor
+	 * fb in use, simply avoid advertising support for 256x256 cursors.
+	 */
+	if (disp->disp->object.oclass >= GM107_DISP) {
 		dev->mode_config.cursor_width = 256;
 		dev->mode_config.cursor_height = 256;
+	} else if (disp->disp->object.oclass >= GK104_DISP) {
+		dev->mode_config.cursor_width = 128;
+		dev->mode_config.cursor_height = 128;
 	} else {
 		dev->mode_config.cursor_width = 64;
 		dev->mode_config.cursor_height = 64;
-- 
2.29.2