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

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Correctness: Good**

The register offsets used in `gv100_head_rgpos` (0x616330, 0x616334) and `gv100_head_state` (0x682064, 0x682068, 0x68206c, 0x682070, 0x68200c, 0x682004) are display head registers that have been stable across GV100 and later generations. The r535 GSP-RM path covers Turing (TU102) and later GPUs, all of which are post-GV100, so these register offsets are appropriate. The existing `gv100_head` function table (`gv100.c:300`) uses the exact same `.state` and `.rgpos` functions, confirming compatibility.

**The fix itself:**

1. `gv100.c` — Removing `static` from `gv100_head_rgpos` and `gv100_head_state` is the minimal change needed to export them. Good.

2. `head.h` — The new declarations:
   ```c
   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);
   ```
   These are placed correctly alongside the other `gv100_head_*` declarations and match the function signatures in `nvkm_head_func`.

3. `r535/disp.c` — The empty stub removal and wiring:
   ```c
   r535_head = {
       .state = gv100_head_state,
       .rgpos = gv100_head_rgpos,
       .vblank_get = r535_head_vblank_get,
       .vblank_put = r535_head_vblank_put,
   };
   ```
   Clean removal of the no-op `r535_head_state` and addition of `.rgpos`. The function table now mirrors `gv100_head` (minus `.rgclk` which isn't needed in the GSP path since GSP handles clock setup).

**Minor nits (non-blocking):**

- The header declarations use named parameters (`struct nvkm_head *head`, `u16 *hline`) while the existing declarations in the same header use unnamed parameters (`struct nvkm_head *`, `u16 *`). Compare with `nv50_head_rgpos` at `head.h:48`. This is purely cosmetic and doesn't affect correctness, but matching the existing style would be slightly cleaner.

**Stable tag:** The `Cc: <stable@vger.kernel.org> # v6.7+` is appropriate since the Fixes tag points to the r535 initial support commit which landed in v6.7.

**Reviewed-by worthy:** Yes. The patch is correct, minimal, and well-motivated.

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Generated by Claude Code Patch Reviewer