crc32: select an algorithm via Kconfig

Allow the kernel builder to choose a crc32* algorithm for the kernel.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Bob Pearson <rpearson@systemfabricworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 61 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index 6d7ce4b138c4..43359bb1ca90 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -80,6 +80,49 @@ config CRC32_SELFTEST
           and crc32_be over byte strings with random alignment and length
           and computes the total elapsed time and number of bytes processed.
 
+choice
+        prompt "CRC32 implementation"
+        depends on CRC32
+        default CRC32_SLICEBY8
+
+config CRC32_SLICEBY8
+        bool "Slice by 8 bytes"
+        help
+          Calculate checksum 8 bytes at a time with a clever slicing algorithm.
+          This is the fastest algorithm, but comes with a 8KiB lookup table.
+          Most modern processors have enough cache to hold this table without
+          thrashing the cache.
+
+          This is the default implementation choice.  Choose this one unless
+          you have a good reason not to.
+
+config CRC32_SLICEBY4
+        bool "Slice by 4 bytes"
+        help
+          Calculate checksum 4 bytes at a time with a clever slicing algorithm.
+          This is a bit slower than slice by 8, but has a smaller 4KiB lookup
+          table.
+
+          Only choose this option if you know what you are doing.
+
+config CRC32_SARWATE
+        bool "Sarwate's Algorithm (one byte at a time)"
+        help
+          Calculate checksum a byte at a time using Sarwate's algorithm.  This
+          is not particularly fast, but has a small 256 byte lookup table.
+
+          Only choose this option if you know what you are doing.
+
+config CRC32_BIT
+        bool "Classic Algorithm (one bit at a time)"
+        help
+          Calculate checksum one bit at a time.  This is VERY slow, but has
+          no lookup table.  This is provided as a debugging option.
+
+          Only choose this option if you are debugging crc32.
+
+endchoice
+
 config CRC7
         tristate "CRC7 functions"
         help
diff --git a/lib/crc32defs.h b/lib/crc32defs.h
index 6fd191732fec..64cba2c3c700 100644
--- a/lib/crc32defs.h
+++ b/lib/crc32defs.h
@@ -13,6 +13,24 @@
  */
 #define CRC32C_POLY_LE 0x82F63B78
 
+/* Try to choose an implementation variant via Kconfig */
+#ifdef CONFIG_CRC32_SLICEBY8
+# define CRC_LE_BITS 64
+# define CRC_BE_BITS 64
+#endif
+#ifdef CONFIG_CRC32_SLICEBY4
+# define CRC_LE_BITS 32
+# define CRC_BE_BITS 32
+#endif
+#ifdef CONFIG_CRC32_SARWATE
+# define CRC_LE_BITS 8
+# define CRC_BE_BITS 8
+#endif
+#ifdef CONFIG_CRC32_BIT
+# define CRC_LE_BITS 1
+# define CRC_BE_BITS 1
+#endif
+
 /*
  * How many bits at a time to use.  Valid values are 1, 2, 4, 8, 32 and 64.
  * For less performance-sensitive, use 4 or 8 to save table size.