nvc0: always keep TSC slot 0 bound to fix TXF

Same as on nv50, the TXF op always uses the TSC bound to slot 0,
returning blank values if nothing is bound.

An earlier change arranges for the TSC entries list to always have valid
data at entry 0, so here we just make use of it.

Fixes arb_texture_buffer_object-subdata-sync among others.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/gallium/drivers/nouveau/nvc0/nvc0_context.c

@@ -488,6 +488,14 @@ nvc0_create(struct pipe_screen *pscreen, void *priv, unsigned ctxflags)
    if (!screen->tsc.entries[0])
       nvc0_upload_tsc0(nvc0);
 
+   // On Fermi, mark samplers dirty so that the proper binding can happen
+   if (screen->base.class_3d < NVE4_3D_CLASS) {
+      for (int s = 0; s < 6; s++)
+         nvc0->samplers_dirty[s] = 1;
+      nvc0->dirty_3d |= NVC0_NEW_3D_SAMPLERS;
+      nvc0->dirty_cp |= NVC0_NEW_CP_SAMPLERS;
+   }
+
    return pipe;
 
 out_err:

src/gallium/drivers/nouveau/nvc0/nvc0_tex.c

@@ -657,6 +657,19 @@ nvc0_validate_tsc(struct nvc0_context *nvc0, int s)
 
    nvc0->state.num_samplers[s] = nvc0->num_samplers[s];
 
+   // TXF, in unlinked tsc mode, will always use sampler 0. So we have to
+   // ensure that it remains bound. Its contents don't matter, all samplers we
+   // ever create have the SRGB_CONVERSION bit set, so as long as the first
+   // entry is initialized, we're good to go. This is the only bit that has
+   // any effect on what TXF does.
+   if ((nvc0->samplers_dirty[s] & 1) && !nvc0->samplers[s][0]) {
+      if (n == 0)
+         n = 1;
+      // We're guaranteed that the first command refers to the first slot, so
+      // we're not overwriting a valid entry.
+      commands[0] = (0 << 12) | (0 << 4) | 1;
+   }
+
    if (n) {
       if (unlikely(s == 5))
          BEGIN_NIC0(push, NVC0_CP(BIND_TSC), n);