drm/nouveau/clk/gk20a: only restore divider to 1:1 if needed

Only restore the 1:1 divider if it is not set already. Also use the
proper masks for this operation and add a second write as done in the
Android code.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
index e72e20a0d009..0746bb3e3075 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
@@ -429,9 +429,16 @@ _gk20a_pllg_program_mnp(struct gk20a_clk *clk, bool allow_slide)
 
         /* restore out divider 1:1 */
         val = nvkm_rd32(device, GPC2CLK_OUT);
-        val &= ~GPC2CLK_OUT_VCODIV_MASK;
-        udelay(2);
-        nvkm_wr32(device, GPC2CLK_OUT, val);
+        if ((val & GPC2CLK_OUT_VCODIV_MASK) !=
+            (GPC2CLK_OUT_VCODIV1 << GPC2CLK_OUT_VCODIV_SHIFT)) {
+                val &= ~GPC2CLK_OUT_VCODIV_MASK;
+                val |= GPC2CLK_OUT_VCODIV1 << GPC2CLK_OUT_VCODIV_SHIFT;
+                udelay(2);
+                nvkm_wr32(device, GPC2CLK_OUT, val);
+                /* Intentional 2nd write to assure linear divider operation */
+                nvkm_wr32(device, GPC2CLK_OUT, val);
+                nvkm_rd32(device, GPC2CLK_OUT);
+        }
 
         /* slide up to new NDIV */
         return allow_slide ? gk20a_pllg_slide(clk, clk->n) : 0;