drm/nv50/gr: enable ctxprog xfer only when we need it to save power

This patch adds instructions to ctxprog and by doing, impacts context
switching performance.  My testcase showed a 1% performance cost using
glxgears that is a context-switch bound application.

Please test and report bugs/performance/power/other.

Many thanks to Maxim Levitsky for his dedicated work on lowering power
consumption with nouveau.

More patches are coming thanks to his work:

https://bugs.freedesktop.org/show_bug.cgi?id=37922

Signed-off-by: Martin Peres <martin.peres@ensi-bourges.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nv50_grctx.c b/drivers/gpu/drm/nouveau/nv50_grctx.c
index e04fb4483c5..d05c2c3b244 100644
--- a/drivers/gpu/drm/nouveau/nv50_grctx.c
+++ b/drivers/gpu/drm/nouveau/nv50_grctx.c
@@ -40,6 +40,9 @@
 #define CP_FLAG_UNK0B                 ((0 * 32) + 0xb)
 #define CP_FLAG_UNK0B_CLEAR           0
 #define CP_FLAG_UNK0B_SET             1
+#define CP_FLAG_XFER_SWITCH           ((0 * 32) + 0xe)
+#define CP_FLAG_XFER_SWITCH_DISABLE   0
+#define CP_FLAG_XFER_SWITCH_ENABLE    1
 #define CP_FLAG_STATE                 ((0 * 32) + 0x1c)
 #define CP_FLAG_STATE_STOPPED         0
 #define CP_FLAG_STATE_RUNNING         1
@@ -199,6 +202,7 @@ nv50_grctx_init(struct nouveau_grctx *ctx)
         }
 
         cp_set (ctx, STATE, RUNNING);
+        cp_set (ctx, XFER_SWITCH, ENABLE);
         /* decide whether we're loading/unloading the context */
         cp_bra (ctx, AUTO_SAVE, PENDING, cp_setup_save);
         cp_bra (ctx, USER_SAVE, PENDING, cp_setup_save);
@@ -265,6 +269,7 @@ nv50_grctx_init(struct nouveau_grctx *ctx)
         cp_name(ctx, cp_exit);
         cp_set (ctx, USER_SAVE, NOT_PENDING);
         cp_set (ctx, USER_LOAD, NOT_PENDING);
+        cp_set (ctx, XFER_SWITCH, DISABLE);
         cp_set (ctx, STATE, STOPPED);
         cp_out (ctx, CP_END);
         ctx->ctxvals_pos += 0x400; /* padding... no idea why you need it */