[BNX2]: Add write posting comment.

Add comment to explain why we cannot read back after chip reset
before delaying.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bnx2.c

@@ -3934,6 +3934,10 @@ bnx2_reset_chip(struct bnx2 *bp, u32 reset_code)
 		/* Chip reset. */
 		REG_WR(bp, BNX2_PCICFG_MISC_CONFIG, val);
 
+		/* Reading back any register after chip reset will hang the
+		 * bus on 5706 A0 and A1.  The msleep below provides plenty
+		 * of margin for write posting.
+		 */
 		if ((CHIP_ID(bp) == CHIP_ID_5706_A0) ||
 		    (CHIP_ID(bp) == CHIP_ID_5706_A1))
 			msleep(20);