drm/nv50-/disp: Use output specific mask in interrupt

The commit

   commit 476e84e126171d809f9c0b5d97137f5055f95ca8
   Author: Ben Skeggs <bskeggs@redhat.com>
   Date:   Mon Feb 11 09:24:23 2013 +1000

       drm/nv50-/disp: initial supervisor support for off-chip encoders

changed the write mask in one of the interrupt functions for on-chip encoders,
causing a regression in certain VGA dual-head setups. This commit reintroduces
the mask thus resolving the regression

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66129
Reported-and-Tested-by: Yves-Alexis <corsac@debian.org>
Cc: stable@vger.kernel.org [3.9+]
CC: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/engine/disp/nv50.c

@@ -1107,6 +1107,7 @@ nv50_disp_intr_unk20_2(struct nv50_disp_priv *priv, int head)
 	u32 pclk = nv_rd32(priv, 0x610ad0 + (head * 0x540)) & 0x3fffff;
 	u32 hval, hreg = 0x614200 + (head * 0x800);
 	u32 oval, oreg;
+	u32 mask;
 	u32 conf = exec_clkcmp(priv, head, 0xff, pclk, &outp);
 	if (conf != ~0) {
 		if (outp.location == 0 && outp.type == DCB_OUTPUT_DP) {
@@ -1133,6 +1134,7 @@ nv50_disp_intr_unk20_2(struct nv50_disp_priv *priv, int head)
 			oreg = 0x614280 + (ffs(outp.or) - 1) * 0x800;
 			oval = 0x00000000;
 			hval = 0x00000000;
+			mask = 0xffffffff;
 		} else
 		if (!outp.location) {
 			if (outp.type == DCB_OUTPUT_DP)
@@ -1140,14 +1142,16 @@ nv50_disp_intr_unk20_2(struct nv50_disp_priv *priv, int head)
 			oreg = 0x614300 + (ffs(outp.or) - 1) * 0x800;
 			oval = (conf & 0x0100) ? 0x00000101 : 0x00000000;
 			hval = 0x00000000;
+			mask = 0x00000707;
 		} else {
 			oreg = 0x614380 + (ffs(outp.or) - 1) * 0x800;
 			oval = 0x00000001;
 			hval = 0x00000001;
+			mask = 0x00000707;
 		}
 
 		nv_mask(priv, hreg, 0x0000000f, hval);
-		nv_mask(priv, oreg, 0x00000707, oval);
+		nv_mask(priv, oreg, mask, oval);
 	}
 }