| Message ID | 1481076574-54711-2-git-send-email-christopher.lee.bostic@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Dec 06, 2016 at 08:09:31PM -0600, Chris Bostic wrote: > From: Jeremy Kerr <jk@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. > > 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@ozlabs.org> > Signed-off-by: Chris Bostic <cbostic@us.ibm.com> > --- > drivers/fsi/fsi-core.c | 21 +++++++++++++++++++++ > drivers/fsi/fsi-master.h | 21 +++++++++++++++++++++ > 2 files changed, 42 insertions(+) Why not just create lib/crc4.c with these functions, like the other crc functions in the kernel? Don't bury these in some random driver subsystem please. thanks, greg k-h
Hi Greg, > Why not just create lib/crc4.c with these functions, like the other crc > functions in the kernel? Two (bad) reasons: - The crc4 implementation here is pretty specific to the FSI usage (only supporting 4-bit-sized chunks), to keep the math & lookup table simple - I'm lazy So yes, we should spend the effort now to make this generic enough for a lib/crc4.c. Would we want to support different values for the polynomial? Chris: do you want me to to that, or will you? Cheers, Jeremy
On Wed, Dec 7, 2016 at 5:33 PM, Jeremy Kerr <jk@ozlabs.org> wrote: > Hi Greg, > >> Why not just create lib/crc4.c with these functions, like the other crc >> functions in the kernel? > > Two (bad) reasons: > > - The crc4 implementation here is pretty specific to the FSI > usage (only supporting 4-bit-sized chunks), to keep the math & lookup > table simple > > - I'm lazy > > So yes, we should spend the effort now to make this generic enough for > a lib/crc4.c. Would we want to support different values for the > polynomial? > > Chris: do you want me to to that, or will you? Hi Jeremy, I'll take this one. Will implement as per Greg's suggestions. Thanks, Chris > > Cheers, > > > Jeremy
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 */