drm/nouveau/fbcon: using nv_two_heads is not a good idea

commit 9bd0c15fcfb42f6245447c53347d65ad9e72080b upstream.

nv_two_heads() was never meant to be used outside of pre-nv50 code.  The
code checks for >= NV_10 for 2 CRTCs, then downgrades a few specific
chipsets to 1 CRTC based on (pci_device & 0x0ff0).

The breakage example seen is on GTX 560Ti, with a pciid of 0x1200, which
gets detected as an NV20 (0x020x) with 1 CRTC by nv_two_heads(), causing
memory corruption because there's actually 2 CRTCs..

This switches fbcon to use the CRTC count directly from the mode_config
structure, which will also fix the same issue on Kepler boards which have
4 CRTCs.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
index 3a4cc32..cc0801d 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
@@ -499,7 +499,7 @@ int nouveau_fbcon_init(struct drm_device *dev)
        nfbdev->helper.funcs = &nouveau_fbcon_helper_funcs;
 
        ret = drm_fb_helper_init(dev, &nfbdev->helper,
-                                nv_two_heads(dev) ? 2 : 1, 4);
+                                dev->mode_config.num_crtc, 4);
        if (ret) {
                kfree(nfbdev);
                return ret;