[PATCH linux v4 09/20] fsi: Add crc4 helpers

[christopher.lee.bostic at gmail.com]

From: Jeremy Kerr <jk at ozlabs.org>

Add some helpers for the crc checks for the slave configuration table.
This works 4-bits-at-a-time, using a simple table approach.

Signed-off-by: Jeremy Kerr <jk at ozlabs.org>
---
 drivers/fsi/fsi-core.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
index 9744a55..24538ae 100644
--- a/drivers/fsi/fsi-core.c
+++ b/drivers/fsi/fsi-core.c
@@ -34,6 +34,29 @@ struct fsi_slave {
 
 #define to_fsi_slave(d) container_of(d, struct fsi_slave, dev)
 
+/* crc helpers */
+static const uint8_t crc4_tab[] = {
+	0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2,
+	0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
+};
+
+static uint8_t crc4(uint32_t x)
+{
+	uint8_t c = 0;
+	int i;
+
+	/* Calculate crc4 over four-bit nibbles, starting at the MSbit */
+	for (i = 28; i >= 0; i -= 4)
+		c = crc4_tab[c ^ ((x >> i) & 0xf)];
+
+	return c;
+}
+
+static bool check_crc4(uint32_t x)
+{
+	return crc4(x) == 0;
+}
+
 /* FSI slave support */
 static int fsi_slave_init(struct fsi_master *master,
 		int link, uint8_t slave_id)
-- 
1.8.2.2