vgsp: X/GL frame-pacer mirror (sema_xw_mirror) - unblocks the 10s/frame stall

r861 evidence: the X server's present path spins in a 10s-timeout wait
((EE) NVIDIA(GPU-0): WAIT (2, 8, 0x8000, <stuck 0xd4..>, <driver counter
+0x70/frame>)) comparing (progress_word & 0x3ffff) << 2 against its own
submitted-byte counter; the progress word (lone u32 0x140235 in an
otherwise-zero guest page) never advances because the emulation does not
execute the 2D method streams -> glxgears 0.09 FPS. A gdb write of the
word to 0x140000 | (counter >> 2) made the wait complete in 3 ms
(WAIT (0, ... <equal>, <equal>) immediately after the timeout print) and
silenced all further timeouts. This adds a 3 ms kthread that mirrors the
driver's counter word into the progress word; both guest PAs are injected
per boot via the sema_xw_mirror parameter (0,0 stops). Demo-path tuning
aid; no product logic depends on it.

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/gsp_sema_service.h b/kernel/gsp_sema_service.h
index 2184826..e96ce1c 100644
--- a/kernel/gsp_sema_service.h
+++ b/kernel/gsp_sema_service.h
@@ -133,6 +133,7 @@ int  gsp_sema_service_walk_probe(u64 gpu_va);
 int  gsp_sema_service_dump_channels(void);
 int  gsp_sema_service_add_map(u64 gpu_va, u64 pa, u64 len, u32 ap);
 int  gsp_sema_service_dump_vidmem(u64 addr, u64 len);
+int  gsp_sema_service_xw_mirror(u64 cnt_pa, u64 mem_pa);
 int  gsp_sema_service_find_vidmem(u64 pattern, u64 max_hits);
 int  gsp_sema_service_pdb_discover(u64 ring_va, u64 ring_pa);
 int  gsp_sema_service_chan_rewind(u32 h_object);