[PATCH linux v4 14/20] drivers/fsi: CRC Utility Updates

[christopher.lee.bostic at gmail.com]

From: Chris Bostic <cbostic at us.ibm.com>

Provided by Jeremy Kerr.  Revise the CRC calculation utilities
to take variable bit length input.

Signed-off-by: Chris Bostic <cbostic at us.ibm.com>
---
 drivers/fsi/fsi-core.c   | 16 +++++++++-------
 drivers/fsi/fsi-master.h | 21 +++++++++++++++++++++
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
index 10bf817..07f5034 100644
--- a/drivers/fsi/fsi-core.c
+++ b/drivers/fsi/fsi-core.c
@@ -111,21 +111,23 @@ static const uint8_t crc4_tab[] = {
 	0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3,
 };
 
-static uint8_t crc4(uint32_t x)
+uint8_t fsi_crc4(uint8_t c, uint64_t x, int bits)
 {
-	uint8_t c = 0;
 	int i;
 
+	/* ALign to 4-bits */
+	bits = (bits + 3) & ~0x3;
+
 	/* Calculate crc4 over four-bit nibbles, starting at the MSbit */
-	for (i = 28; i >= 0; i -= 4)
+	for (i = bits; i >= 0; i -= 4)
 		c = crc4_tab[c ^ ((x >> i) & 0xf)];
 
 	return c;
 }
 
-static bool check_crc4(uint32_t x)
+static bool check_crc4_u32(uint32_t x)
 {
-	return crc4(x) == 0;
+	return fsi_crc4(0, x, 32) == 0;
 }
 
 /* FSI slave support */
@@ -171,7 +173,7 @@ static int fsi_slave_scan(struct fsi_slave *slave)
 
 		conf = be32_to_cpu(conf);
 
-		if (!check_crc4(conf)) {
+		if (!check_crc4_u32(conf)) {
 			dev_warn(&slave->dev,
 				"crc error in slave register at 0x%04x\n",
 					i);
@@ -247,7 +249,7 @@ static int fsi_slave_init(struct fsi_master *master,
 	}
 
 	chip_id = be32_to_cpu(chip_id);
-	if (!check_crc4(chip_id)) {
+	if (!check_crc4_u32(chip_id)) {
 		dev_warn(master->dev, "slave %02x:%02x: invalid chip id CRC!\n",
 				link, slave_id);
 		return -EIO;
diff --git a/drivers/fsi/fsi-master.h b/drivers/fsi/fsi-master.h
index e75a810..cafb433 100644
--- a/drivers/fsi/fsi-master.h
+++ b/drivers/fsi/fsi-master.h
@@ -34,4 +34,25 @@ struct fsi_master {
 extern int fsi_master_register(struct fsi_master *master);
 extern void fsi_master_unregister(struct fsi_master *master);
 
+/**
+ * crc4 helper: Given a starting crc4 state @c, calculate the crc4 vaue of @x,
+ * which is @bits in length. This may be required by master implementations
+ * that do not provide their own hardware checksums.
+ *
+ * The crc4 is performed on 4-bit chunks (which is all we need for FSI
+ * calculations). Typically, we'll want a starting state of 0:
+ *
+ *  c = fsi_crc4(0, msg, len);
+ *
+ * To crc4 a message that includes a single start bit, initialise crc4 state
+ * with:
+ *
+ *  c = fsi_crc4(0, 1, 1);
+ *
+ * Then update with message data:
+ *
+ *  c = fsi_crc4(c, msg, len);
+ */
+uint8_t fsi_crc4(uint8_t c, uint64_t x, int bits);
+
 #endif /* DRIVERS_FSI_MASTER_H */
-- 
1.8.2.2