RE: [RFC] bmac:change to use bitrev8() generic function

From: Tobias Klauser
Sent: 10 August 2015 12:49
On 2015-08-10 at 11:53:41 +0200, yalin wang [off-list ref] wrote:

quoted

This change to use generic bitrev8() for bmac driver.

...

quoted

@@ -871,7 +860,7 @@ bmac_addhash(struct bmac_data *bp, unsigned char *addr)

 	if (!(*addr)) return;
 	crc = bmac_crc((unsigned short *)addr) & 0x3f; /* Big-endian alert! */

Why not *((u8 *)addr + 1) & 0x3f

quoted

-	crc = reverse6[crc];	/* Hyperfast bit-reversing algorithm */
+	crc = bitrev8((u8)crc);

No, this won't work. reverse6 works on 6 bit values, while bitrev8 works
on 8bit values, e.g. reverse6[1] = 0x20, while bitrev8(1) = 0x80

You could use bitrev8(n) >> 2.

But that is a 'strange' map of a 7-bit value to a 6-bit one.

I thought it was more common for ethernet hardware to use the
value of the crc register after all 6 bytes of the mac address
had been processed.

	David