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>

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index 4d57bba..30f9453 100644 (file)
--- 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 39787db..e824d08 100644 (file)
--- 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");