powerpc/mm: Add a CONFIG option to choose if radix is used by default

Currently if the hardware supports the radix MMU we will use
it, *unless* "disable_radix" is passed on the kernel command line.

However some users would like the reverse semantics. ie. The kernel
uses the hash MMU by default, unless radix is explicitly requested on
the command line.

So add a CONFIG option to choose whether we use radix by default or
not, and expand the disable_radix command line option to allow
"disable_radix=no" which *enables* radix.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 11 insertions, 2 deletions

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 12b3025fadac..a07722531b32 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -368,10 +368,19 @@ EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
 #endif /* CONFIG_SPARSEMEM_VMEMMAP */
 
 #ifdef CONFIG_PPC_BOOK3S_64
-static bool disable_radix;
+static bool disable_radix = !IS_ENABLED(CONFIG_PPC_RADIX_MMU_DEFAULT);
+
 static int __init parse_disable_radix(char *p)
 {
-	disable_radix = true;
+	bool val;
+
+	if (strlen(p) == 0)
+		val = true;
+	else if (kstrtobool(p, &val))
+		return -EINVAL;
+
+	disable_radix = val;
+
 	return 0;
 }
 early_param("disable_radix", parse_disable_radix);