From: Jeremy Kerr <jk@xxxxxxxxxx>
Add some helpers for the crc checks for the slave configuration table.
This works 4-bits-at-a-time, using a simple table approach.
We will need this in the FSI core code, as well as any master
implementations that need to calculate CRCs in software.
Signed-off-by: Jeremy Kerr <jk@xxxxxxxxxx>
Signed-off-by: Chris Bostic <cbostic@xxxxxxxxxx>
---
drivers/fsi/fsi-core.c | 21 +++++++++++++++++++++
drivers/fsi/fsi-master.h | 21 +++++++++++++++++++++
2 files changed, 42 insertions(+)
diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
index ceaf536..f0832c7 100644
--- a/drivers/fsi/fsi-core.c
+++ b/drivers/fsi/fsi-core.c
@@ -32,6 +32,27 @@ 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,
+};
+
+uint8_t fsi_crc4(uint8_t c, uint64_t x, int bits)
+{
+ int i;
+
+ /* Align to 4-bits */
+ bits = (bits + 3) & ~0x3;
+
+ /* Calculate crc4 over four-bit nibbles, starting at the MSbit */
+ for (i = bits; i >= 0; i -= 4)
+ c = crc4_tab[c ^ ((x >> i) & 0xf)];
+
+ return c;
+}
+EXPORT_SYMBOL_GPL(fsi_crc4);
+
/* FSI slave support */
static int fsi_slave_init(struct fsi_master *master,
int link, uint8_t slave_id)
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
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