nvfx: add NOUVEAU_VTXIDX_IN_VRAM variable to put vertex/index buffers in VRAM

On some systems, putting vertex and index buffers in VRAM instead of GART
memory eliminates massive graphics corruption which is otherwise present,
due to unclear causes.

This patch adds an environment variable that does that, along with helpful
messages.

It turns it on by default on G7x, as it is what I am seeing corruption
on and some other reports also seemed to pinpoint these cards.

1 files changed, 31 insertions, 0 deletions

diff --git a/src/gallium/drivers/nvfx/nvfx_screen.c b/src/gallium/drivers/nvfx/nvfx_screen.c
index 6cbd8b23e1..f7f3921894 100644
--- a/src/gallium/drivers/nvfx/nvfx_screen.c
+++ b/src/gallium/drivers/nvfx/nvfx_screen.c
@@ -293,6 +293,36 @@ static void nv40_screen_init(struct nvfx_screen *screen, struct nouveau_stateobj
 	so_data  (so, 0x00000001);
 }
 
+static void
+nvfx_screen_init_buffer_functions(struct nvfx_screen* screen)
+{
+	int vram_hack_default = 0;
+	int vram_hack;
+	// TODO: this is a bit of a guess; also add other cards that may need this hack.
+	// It may also depend on the specific card or the AGP/PCIe chipset.
+	if(screen->base.device->chipset == 0x47 /* G70 */
+		|| screen->base.device->chipset == 0x49 /* G71 */
+		|| screen->base.device->chipset == 0x46 /* G72 */
+		)
+		vram_hack_default = 1;
+	vram_hack = debug_get_bool_option("NOUVEAU_VTXIDX_IN_VRAM", vram_hack_default);
+
+#ifdef DEBUG
+	if(!vram_hack)
+	{
+		fprintf(stderr, "Some systems may experience graphics corruption due to randomly misplaced vertices.\n"
+			"If this is happening, export NOUVEAU_VTXIDX_IN_VRAM=1 may reduce or eliminate the problem\n");
+	}
+	else
+	{
+		fprintf(stderr, "A performance reducing hack is being used to help avoid graphics corruption.\n"
+			"You can try export NOUVEAU_VTXIDX_IN_VRAM=0 to disable it.\n");
+	}
+#endif
+
+	screen->vertex_buffer_flags = vram_hack ? NOUVEAU_BO_VRAM : NOUVEAU_BO_GART;
+}
+
 struct pipe_screen *
 nvfx_screen_create(struct pipe_winsys *ws, struct nouveau_device *dev)
 {
@@ -350,6 +380,7 @@ nvfx_screen_create(struct pipe_winsys *ws, struct nouveau_device *dev)
 		return NULL;
 	}
 
+	nvfx_screen_init_buffer_functions(screen);
 	nvfx_screen_init_miptree_functions(pscreen);
 
 	ret = nouveau_grobj_alloc(chan, 0xbeef3097, eng3d_class, &screen->eng3d);