1 files changed, 25 insertions, 0 deletions

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index c39200161688..ca4629f66d17 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -419,6 +419,31 @@ static void agp_v2_parse_one(u32 *requested_mode, u32 *bridge_agpstat, u32 *vga_
                 *requested_mode &= ~AGP2_RESERVED_MASK;
         }
 
+        /*
+         * Some dumb bridges are programmed to disobey the AGP2 spec.
+         * This is likely a BIOS misprogramming rather than poweron default, or
+         * it would be a lot more common.
+         * https://bugs.freedesktop.org/show_bug.cgi?id=8816
+         * AGPv2 spec 6.1.9 states:
+         *   The RATE field indicates the data transfer rates supported by this
+         *   device. A.G.P. devices must report all that apply.
+         * Fix them up as best we can.
+         */
+        switch (*bridge_agpstat & 7) {
+        case 4:
+                *bridge_agpstat |= (AGPSTAT2_2X | AGPSTAT2_1X);
+                printk(KERN_INFO PFX "BIOS bug. AGP bridge claims to only support x4 rate"
+                        "Fixing up support for x2 & x1\n");
+                break;
+        case 2:
+                *bridge_agpstat |= AGPSTAT2_1X;
+                printk(KERN_INFO PFX "BIOS bug. AGP bridge claims to only support x2 rate"
+                        "Fixing up support for x1\n");
+                break;
+        default:
+                break;
+        }
+
         /* Check the speed bits make sense. Only one should be set. */
         tmp = *requested_mode & 7;
         switch (tmp) {