powerpc/watchpoint/ptrace: Introduce PPC_DEBUG_FEATURE_DATA_BP_ARCH_31

PPC_DEBUG_FEATURE_DATA_BP_ARCH_31 can be used to determine whether
we are running on an ISA 3.1 compliant machine. Which is needed to
determine DAR behaviour, 512 byte boundary limit etc. This was
requested by Pedro Miraglia Franco de Carvalho for extending
watchpoint features in gdb. Note that availability of 2nd DAWR is
independent of this flag and should be checked using
ppc_debug_info->num_data_bps.
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/20200902042945.129369-8-ravi.bangoria@linux.ibm.com

Documentation/powerpc/ptrace.rst

@@ -46,6 +46,7 @@ features will have bits indicating whether there is support for::
   #define PPC_DEBUG_FEATURE_DATA_BP_RANGE		0x4
   #define PPC_DEBUG_FEATURE_DATA_BP_MASK		0x8
   #define PPC_DEBUG_FEATURE_DATA_BP_DAWR		0x10
+  #define PPC_DEBUG_FEATURE_DATA_BP_ARCH_31		0x20
 
 2. PTRACE_SETHWDEBUG
 

arch/powerpc/include/uapi/asm/ptrace.h

@@ -222,6 +222,7 @@ struct ppc_debug_info {
 #define PPC_DEBUG_FEATURE_DATA_BP_RANGE		0x0000000000000004
 #define PPC_DEBUG_FEATURE_DATA_BP_MASK		0x0000000000000008
 #define PPC_DEBUG_FEATURE_DATA_BP_DAWR		0x0000000000000010
+#define PPC_DEBUG_FEATURE_DATA_BP_ARCH_31	0x0000000000000020
 
 #ifndef __ASSEMBLY__
 

arch/powerpc/kernel/ptrace/ptrace-noadv.c

@@ -57,6 +57,8 @@ void ppc_gethwdinfo(struct ppc_debug_info *dbginfo)
 	} else {
 		dbginfo->features = 0;
 	}
+	if (cpu_has_feature(CPU_FTR_ARCH_31))
+		dbginfo->features |= PPC_DEBUG_FEATURE_DATA_BP_ARCH_31;
 }
 
 int ptrace_get_debugreg(struct task_struct *child, unsigned long addr,