drm/nouveau/disp/r535: Add scanline position support + head state support

That's right! It looks like this never actually got finished, something
which I just noticed today when I saw this fun message spamming one of my
test machine's kernel logs when enabling display debug output for nouveau:

  [drm:drm_crtc_vblank_helper_get_vblank_timestamp_internal] crtc 0 : scanoutpos query failed.

So it looks like we've been falling back to DRM's core fallback for a while
now, whoops.

So, while it seems that we do have the option of doing this through GSP -
that doesn't seem like a great idea. Mainly because reading this from GSP
would involve a lot more latency then we should have for vblank handling
due to the RPC communication. So instead of implementing that, just use
gv100_head_state and gv100_head_rgpos for implementing .state and .rgpos.
It seems to work perfectly fine!

Fixes: 9e99444490 ("drm/nouveau/disp/r535: initial support")
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Timur Tabi <ttabi@nvidia.com>
Cc: Ben Skeggs <bskeggs@nvidia.com>
Cc: James Jones <jajones@nvidia.com>
Cc: Faith Ekstrand <faith.ekstrand@collabora.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Aaron Kling <webgeek1234@gmail.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Zhang Enpei <zhang.enpei@zte.com.cn>
Cc: <stable@vger.kernel.org> # v6.7+
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patch.msgid.link/20260429030348.3930866-1-lyude@redhat.com
(cherry picked from commit 804cb093b2)
Signed-off-by: Lyude Paul <lyude@redhat.com>

drivers/gpu/drm/nouveau/nvkm/engine/disp/gv100.c

@@ -253,7 +253,7 @@ gv100_head_vblank_get(struct nvkm_head *head)
 	nvkm_mask(device, 0x611d80 + (head->id * 4), 0x00000004, 0x00000004);
 }
 
-static void
+void
 gv100_head_rgpos(struct nvkm_head *head, u16 *hline, u16 *vline)
 {
 	struct nvkm_device *device = head->disp->engine.subdev.device;
@@ -263,7 +263,7 @@ gv100_head_rgpos(struct nvkm_head *head, u16 *hline, u16 *vline)
 	*hline = nvkm_rd32(device, 0x616334 + hoff) & 0x0000ffff;
 }
 
-static void
+void
 gv100_head_state(struct nvkm_head *head, struct nvkm_head_state *state)
 {
 	struct nvkm_device *device = head->disp->engine.subdev.device;

drivers/gpu/drm/nouveau/nvkm/engine/disp/head.h

@@ -53,6 +53,8 @@ void gf119_head_rgclk(struct nvkm_head *, int);
 
 int gv100_head_cnt(struct nvkm_disp *, unsigned long *);
 int gv100_head_new(struct nvkm_disp *, int id);
+void gv100_head_state(struct nvkm_head *head, struct nvkm_head_state *state);
+void gv100_head_rgpos(struct nvkm_head *head, u16 *hline, u16 *vline);
 
 #define HEAD_MSG(h,l,f,a...) do {                                              \
 	struct nvkm_head *_h = (h);                                            \

drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c

@@ -625,14 +625,10 @@ r535_head_vblank_get(struct nvkm_head *head)
 	nvkm_mask(device, 0x611d80 + (head->id * 4), 0x00000002, 0x00000002);
 }
 
-static void
-r535_head_state(struct nvkm_head *head, struct nvkm_head_state *state)
-{
-}
-
 static const struct nvkm_head_func
 r535_head = {
-	.state = r535_head_state,
+	.state = gv100_head_state,
+	.rgpos = gv100_head_rgpos,
 	.vblank_get = r535_head_vblank_get,
 	.vblank_put = r535_head_vblank_put,
 };