amd64_edac: Fix K8 revD and later chip select sizes

Fix DRAM chip select sizes calculation for K8, revisions D and E.

Reported-by: Niklas Söderlund <niklas.soderlund@ericsson.com
Link: http://lkml.kernel.org/r/1320849178-23340-1-git-send-email-niklas.soderlund@ericsson.com
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>

diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
index c9eee6d33e9a70cf5f851570c48ff3086b93c39a..6a83d49c9370ac2e325dbd9a1ace0c48135a73f9 100644 (file)
--- a/drivers/edac/amd64_edac.c
+++ b/drivers/edac/amd64_edac.c
@@ -1132,12 +1132,36 @@ static int k8_dbam_to_chip_select(struct amd64_pvt *pvt, u8 dct,
                return ddr2_cs_size(cs_mode, dclr & WIDTH_128);
        }
        else if (pvt->ext_model >= K8_REV_D) {
+               unsigned diff;
                WARN_ON(cs_mode > 10);
 
-               if (cs_mode == 3 || cs_mode == 8)
-                       return 32 << (cs_mode - 1);
-               else
-                       return 32 << cs_mode;
+               /*
+                * the below calculation, besides trying to win an obfuscated C
+                * contest, maps cs_mode values to DIMM chip select sizes. The
+                * mappings are:
+                *
+                * cs_mode      CS size (mb)
+                * =======      ============
+                * 0            32
+                * 1            64
+                * 2            128
+                * 3            128
+                * 4            256
+                * 5            512
+                * 6            256
+                * 7            512
+                * 8            1024
+                * 9            1024
+                * 10           2048
+                *
+                * Basically, it calculates a value with which to shift the
+                * smallest CS size of 32MB.
+                *
+                * ddr[23]_cs_size have a similar purpose.
+                */
+               diff = cs_mode/3 + (unsigned)(cs_mode > 5);
+
+               return 32 << (cs_mode - diff);
        }
        else {
                WARN_ON(cs_mode > 6);