powerpc/watchpoint: Remove 512 byte boundary

Power10 has removed 512 bytes boundary from match criteria i.e. the watch
range can cross 512 bytes boundary.

Note: ISA 3.1 Book III 9.4 match criteria includes 512 byte limit but that
is a documentation mistake and hopefully will be fixed in the next version
of ISA. Though, ISA 3.1 change log mentions about removal of 512B boundary:

  Multiple DEAW:
  Added a second Data Address Watchpoint. [H]DAR is
  set to the first byte of overlap. 512B boundary is
  removed.
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200723090813.303838-11-ravi.bangoria@linux.ibm.com

arch/powerpc/kernel/hw_breakpoint.c

@@ -418,8 +418,9 @@ static int hw_breakpoint_validate_len(struct arch_hw_breakpoint *hw)
 
 	if (dawr_enabled()) {
 		max_len = DAWR_MAX_LEN;
-		/* DAWR region can't cross 512 bytes boundary */
-		if (ALIGN_DOWN(start_addr, SZ_512) != ALIGN_DOWN(end_addr - 1, SZ_512))
+		/* DAWR region can't cross 512 bytes boundary on p10 predecessors */
+		if (!cpu_has_feature(CPU_FTR_ARCH_31) &&
+		    (ALIGN_DOWN(start_addr, SZ_512) != ALIGN_DOWN(end_addr - 1, SZ_512)))
 			return -EINVAL;
 	} else if (IS_ENABLED(CONFIG_PPC_8xx)) {
 		/* 8xx can setup a range without limitation */