drm/nouveau/devinit/gf100: make devinit on resume safer

In case of successful suspend, devinit will have to be run and this is
the behavior currently hardcoded. However, as FD bug 94725 suggests,
there might be cases where runtime suspend leaves the GPU powered, and
in such cases devinit should not be run on resume.

On GF100+ we have a reliable way to know whether we need to run devinit.
Use it instead of blindly trusting the flag set by nvkm_devinit_fini().

The code around the NvForcePost also needs to be slightly reworked in
order to keep working.
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Suggested-by: Dave Airlie <airlied@redhat.com>
Suggested-by: Karol Herbst <nouveau@karolherbst.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/subdev/devinit.h

@@ -7,6 +7,7 @@ struct nvkm_devinit {
 	const struct nvkm_devinit_func *func;
 	struct nvkm_subdev subdev;
 	bool post;
+	bool force_post;
 };
 
 u32 nvkm_devinit_mmio(struct nvkm_devinit *, u32 addr);

drivers/gpu/drm/nouveau/nvkm/subdev/devinit/base.c

@@ -83,6 +83,12 @@ nvkm_devinit_preinit(struct nvkm_subdev *subdev)
 	if (init->func->preinit)
 		init->func->preinit(init);
 
+	/* Override the post flag during the first call if NvForcePost is set */
+	if (init->force_post) {
+		init->post = init->force_post;
+		init->force_post = false;
+	}
+
 	/* unlock the extended vga crtc regs */
 	nvkm_lockvgac(subdev->device, false);
 	return 0;
@@ -126,5 +132,5 @@ nvkm_devinit_ctor(const struct nvkm_devinit_func *func,
 {
 	nvkm_subdev_ctor(&nvkm_devinit, device, index, 0, &init->subdev);
 	init->func = func;
-	init->post = nvkm_boolopt(device->cfgopt, "NvForcePost", false);
+	init->force_post = nvkm_boolopt(device->cfgopt, "NvForcePost", false);
 }

drivers/gpu/drm/nouveau/nvkm/subdev/devinit/gf100.c

@@ -97,9 +97,11 @@ gf100_devinit_preinit(struct nvkm_devinit *base)
 	struct nvkm_subdev *subdev = &init->base.subdev;
 	struct nvkm_device *device = subdev->device;
 
-	/* This bit is set by devinit, and flips back to 0 on suspend */
-	if (!base->post)
-		base->post = ((nvkm_rd32(device, 0x2240c) & BIT(1)) == 0);
+	/*
+	 * This bit is set by devinit, and flips back to 0 on suspend. We
+	 * can use it as a reliable way to know whether we should run devinit.
+	 */
+	base->post = ((nvkm_rd32(device, 0x2240c) & BIT(1)) == 0);
 }
 
 static const struct nvkm_devinit_func