gxfb/lxfb: detect framebuffer size using an MSR if VSA2 isn't available

If there's no VSA2 (ie, if we're using tinybios or OpenFirmware), use the
GLIU's P2D Range Offset Descriptor to determine how much memory we have
available for the framebuffer.

Originally based on a patch by Jordan Crouse.  Tested with OpenFirmware;
Pascal informs me that tinybios has a stub that fills in P2D_RO0.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 33 insertions, 1 deletions

diff --git a/drivers/video/geode/display_gx.c b/drivers/video/geode/display_gx.c
index 1e82ecc367dd..e759895bf3d3 100644
--- a/drivers/video/geode/display_gx.c
+++ b/drivers/video/geode/display_gx.c
@@ -25,7 +25,23 @@ unsigned int gx_frame_buffer_size(void)
 {
         unsigned int val;
 
-        /* FB size is reported by a virtual register */
+        if (!geode_has_vsa2()) {
+                uint32_t hi, lo;
+
+                /* The number of pages is (PMAX - PMIN)+1 */
+                rdmsr(MSR_GLIU_P2D_RO0, lo, hi);
+
+                /* PMAX */
+                val = ((hi & 0xff) << 12) | ((lo & 0xfff00000) >> 20);
+                /* PMIN */
+                val -= (lo & 0x000fffff);
+                val += 1;
+
+                /* The page size is 4k */
+                return (val << 12);
+        }
+
+        /* FB size can be obtained from the VSA II */
         /* Virtual register class = 0x02 */
         /* VG_MEM_SIZE(512Kb units) = 0x00 */
 
diff --git a/drivers/video/geode/lxfb_ops.c b/drivers/video/geode/lxfb_ops.c
index e42e12489f6d..cd9d4cc26954 100644
--- a/drivers/video/geode/lxfb_ops.c
+++ b/drivers/video/geode/lxfb_ops.c
@@ -329,6 +329,22 @@ unsigned int lx_framebuffer_size(void)
 {
         unsigned int val;
 
+        if (!geode_has_vsa2()) {
+                uint32_t hi, lo;
+
+                /* The number of pages is (PMAX - PMIN)+1 */
+                rdmsr(MSR_GLIU_P2D_RO0, lo, hi);
+
+                /* PMAX */
+                val = ((hi & 0xff) << 12) | ((lo & 0xfff00000) >> 20);
+                /* PMIN */
+                val -= (lo & 0x000fffff);
+                val += 1;
+
+                /* The page size is 4k */
+                return (val << 12);
+        }
+
         /* The frame buffer size is reported by a VSM in VSA II */
         /* Virtual Register Class    = 0x02                     */
         /* VG_MEM_SIZE (1MB units)   = 0x00                     */