From 02ac1be1cc226a8097642e53ccb4c094336cc03c Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Tue, 24 Oct 2017 17:48:49 +0200
Subject: [PATCH] powerpc/mm: Add a CONFIG option to choose if radix is used by
 default

References: bsc#1055186, fate#323286
Patch-mainline: v4.15-rc1
Git-commit: 1fd6c02207107c8892219dacef01de7ced3d4ce7

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>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/mm/init_64.c              | 13 +++++++++++--
 arch/powerpc/platforms/Kconfig.cputype | 13 +++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index f0030973c694..38e12d8af819 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -334,10 +334,19 @@ EXPORT_SYMBOL_GPL(realmode_pfn_to_page);
 #endif /* CONFIG_SPARSEMEM_VMEMMAP/CONFIG_FLATMEM */
 
 #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);
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index f3d219aeb50f..26c084da4c08 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -305,6 +305,19 @@ config PPC_RADIX_MMU
 	  is only implemented by IBM Power9 CPUs, if you don't have one of them
 	  you can probably disable this.
 
+config PPC_RADIX_MMU_DEFAULT
+	bool "Default to using the Radix MMU when possible"
+	depends on PPC_RADIX_MMU
+	default y
+	help
+	  When the hardware supports the Radix MMU, default to using it unless
+	  "disable_radix[=yes]" is specified on the kernel command line.
+
+	  If this option is disabled, the Hash MMU will be used by default,
+	  unless "disable_radix=no" is specified on the kernel command line.
+
+	  If you're unsure, say Y.
+
 config PPC_MMU_NOHASH
 	def_bool y
 	depends on !PPC_STD_MMU
-- 
2.13.6