Re: [PATCH] drm/nouveau/disp/r535: Add scanline position support + head state support

[Dave Airlie]

On Wed, 29 Apr 2026 at 13:04, Lyude Paul <lyude@xxxxxxxxxx> wrote:
>
> 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!

Does the open gpu module do this at all, I'm just mildly worried that
blackwell might have moved stuff,

If you can confirm by looking at open-gpu.

Reviewed-by: Dave Airlie <airlied@xxxxxxxxxx>

Dave.
>
> Fixes: 9e9944449023 ("drm/nouveau/disp/r535: initial support")
> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxxx>
> Cc: Timur Tabi <ttabi@xxxxxxxxxx>
> Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
> Cc: James Jones <jajones@xxxxxxxxxx>
> Cc: Faith Ekstrand <faith.ekstrand@xxxxxxxxxxxxx>
> Cc: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Aaron Kling <webgeek1234@xxxxxxxxx>
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: Zhang Enpei <zhang.enpei@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v6.7+
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/disp/gv100.c       | 4 ++--
>  drivers/gpu/drm/nouveau/nvkm/engine/disp/head.h        | 2 ++
>  drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c | 8 ++------
>  3 files changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/gv100.c b/drivers/gpu/drm/nouveau/nvkm/engine/disp/gv100.c
> index dbd984da75014..0608266188d3e 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/gv100.c
> +++ b/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;
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/head.h b/drivers/gpu/drm/nouveau/nvkm/engine/disp/head.h
> index 856252bf559a4..b642729c254fe 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/head.h
> +++ b/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);                                            \
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c
> index 6e63df816d855..49a1eef9bdf14 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/disp.c
> +++ b/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,
>  };
>
> base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731
> --
> 2.54.0
>