[PATCH] drm/nouveau/devinit/gf100-: try to avoid double-running vbios scripts

[Ilia Mirkin]

Turns out some VBIOSes don't actually set the bit in question in 2240c.
Use the nv50-style detection to try avoiding running the vbios twice.

Fixes: a6a0f67ca7aa ("drm/nouveau/devinit/gf100-: detect if BIOS invoked devinit")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97620
Cc: stable at vger.kernel.org # v4.6+
Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
---

Not sure if this is safe to do esp on GM20x+ boards?

 drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c b/drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c
index 8b1b34c..a568bbf 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c
@@ -102,6 +102,25 @@ gf100_devinit_preinit(struct nvkm_devinit *base)
 	 * can use it as a reliable way to know whether we should run devinit.
 	 */
 	base->post = ((nvkm_rd32(device, 0x2240c) & BIT(1)) == 0);
+
+	/*
+	 * However some VBIOS init sequences miss this bit. So fall back to
+	 * the nv50 method of checking if the bit is not set. Running the
+	 * VBIOS multiple times may have detrimental effects.
+	 */
+	if (base->post) {
+		u64 disable = nvkm_devinit_disable(base);
+		/* magic to detect whether or not x86 vbios code has
+		 * executed the devinit scripts to initialise the
+		 * board. only works if there's a display engine.
+		 */
+		if (!(disable & (1ULL << NVKM_ENGINE_DISP))) {
+			if (nvkm_rdvgac(device, 0, 0x00) ||
+			    nvkm_rdvgac(device, 0, 0x1a)) {
+				base->post = false;
+			}
+		}
+	}
 }
 
 static const struct nvkm_devinit_func
-- 
2.10.2