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-rw-r--r--drivers/char/agp/generic.c25
1 files changed, 25 insertions, 0 deletions
diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index c3920016168..ca4629f66d1 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) {