drm/nouveau/pci/msi: disable MSI on big-endian platforms by default

BugLink: http://bugs.launchpad.net/bugs/1718195

commit bc60c90f upstream.

It appears that MSI does not work on either G5 PPC nor on a E5500-based
platform, where other hardware is reported to work fine with MSI.

Both tests were conducted with NV4x hardware, so perhaps other (or even
this) hardware can be made to work. It's still possible to force-enable
with config=NvMSI=1 on load.
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

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

@@ -180,6 +180,10 @@ nvkm_pci_new_(const struct nvkm_pci_func *func, struct nvkm_device *device,
 		}
 	}
 
+#ifdef __BIG_ENDIAN
+	pci->msi = false;
+#endif
+
 	pci->msi = nvkm_boolopt(device->cfgopt, "NvMSI", pci->msi);
 	if (pci->msi && func->msi_rearm) {
 		pci->msi = pci_enable_msi(pci->pdev) == 0;