lib/raid6: Add log-of-2 table for RAID6 HW requiring disk position

The raid6_gfexp table represents {2}^n values for 0 <= n < 256. The
Linux async_tx framework pass values from raid6_gfexp as coefficients
for each source to prep_dma_pq() callback of DMA channel with PQ
capability. This creates problem for RAID6 offload engines (such as
Broadcom SBA) which take disk position (i.e. log of {2}) instead of
multiplicative cofficients from raid6_gfexp table.

This patch adds raid6_gflog table having log-of-2 value for any given
x such that 0 <= x < 256. For any given disk coefficient x, the
corresponding disk position is given by raid6_gflog[x]. The RAID6
offload engine driver can use this newly added raid6_gflog table to
get disk position from multiplicative coefficient.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Acked-by: Shaohua Li <shli@fb.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index 4d57bbaaa1bf..30f945329818 100644
--- a/include/linux/raid/pq.h
+++ b/include/linux/raid/pq.h
@@ -142,6 +142,7 @@ int raid6_select_algo(void);
 extern const u8 raid6_gfmul[256][256] __attribute__((aligned(256)));
 extern const u8 raid6_vgfmul[256][32] __attribute__((aligned(256)));
 extern const u8 raid6_gfexp[256]      __attribute__((aligned(256)));
+extern const u8 raid6_gflog[256]      __attribute__((aligned(256)));
 extern const u8 raid6_gfinv[256]      __attribute__((aligned(256)));
 extern const u8 raid6_gfexi[256]      __attribute__((aligned(256)));
 
diff --git a/lib/raid6/mktables.c b/lib/raid6/mktables.c
index 39787db588b0..e824d088f72c 100644
--- a/lib/raid6/mktables.c
+++ b/lib/raid6/mktables.c
@@ -125,6 +125,26 @@ int main(int argc, char *argv[])
         printf("EXPORT_SYMBOL(raid6_gfexp);\n");
         printf("#endif\n");
 
+        /* Compute log-of-2 table */
+        printf("\nconst u8 __attribute__((aligned(256)))\n"
+               "raid6_gflog[256] =\n" "{\n");
+        for (i = 0; i < 256; i += 8) {
+                printf("\t");
+                for (j = 0; j < 8; j++) {
+                        v = 255;
+                        for (k = 0; k < 256; k++)
+                                if (exptbl[k] == (i + j)) {
+                                        v = k;
+                                        break;
+                                }
+                        printf("0x%02x,%c", v, (j == 7) ? '\n' : ' ');
+                }
+        }
+        printf("};\n");
+        printf("#ifdef __KERNEL__\n");
+        printf("EXPORT_SYMBOL(raid6_gflog);\n");
+        printf("#endif\n");
+
         /* Compute inverse table x^-1 == x^254 */
         printf("\nconst u8 __attribute__((aligned(256)))\n"
                "raid6_gfinv[256] =\n" "{\n");