[PATCH] agp: Enable all supported rates for graphic cards

[Tormod Volden]

From: Tormod Volden <debian.tormod at gmail.com>

Some cards report that they support only 4x, in which case they
should support 2x and 1x as well, according to the AGP spec.

Otherwise a requested 1x or 2x rate will result in 0 being set:

agpgart-via 0000:00:00.0: putting AGP V2 device into 0x mode

For instance ProSavage KN133 [5333:8d02] only reports 4x.

Signed-off-by: Tormod Volden <debian.tormod at gmail.com>
---
 drivers/char/agp/generic.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index b072648..c5d04e5 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -526,6 +526,24 @@ static void agp_v2_parse_one(u32 *requested_mode, u32 *bridge_agpstat, u32 *vga_
 		break;
 	}
 
+	/* Some graphic cards report they only support 4x, however the AGP 2.0 spec
+	 * (section 4.1.1) says components must support the lower speeds as well.
+	 */
+	switch (*vga_agpstat & 7) {
+	case 4:
+		*vga_agpstat |= (AGPSTAT2_2X | AGPSTAT2_1X);
+		printk(KERN_INFO PFX "Graphics card claims to only support x4 rate. "
+			"Fixing up support for x2 & x1\n");
+		break;
+	case 2:
+		*vga_agpstat |= AGPSTAT2_1X;
+		printk(KERN_INFO PFX "Graphics card 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) {
-- 
1.7.5.4