linux-kernel - [PATCH v2 1/2] MIPS: Allow R6 compact branch policy to be left unspecified

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Date:	Tue, 17 May 2016 15:55:53 +0100
From:	Paul Burton <paul.burton@...tec.com>
To:	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>
CC:	"Maciej W . Rozycki" <Maciej.Rozycki@...tec.com>,
	Paul Burton <paul.burton@...tec.com>,
	"stable # v4 . 4+" <stable@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2 1/2] MIPS: Allow R6 compact branch policy to be left unspecified

It turns out that some toolchains which support MIPS R6 don't support
the -mcompact-branches flag to specify compact branch behaviour. Default
to not providing the -mcompact-branch option to the compiler such that
we can build with such toolchains.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
Reported-by: kbuild test robot <fengguang.wu@...el.com>
Fixes: c1a0e9bc885d ("MIPS: Allow compact branch policy to be changed")
Cc: stable <stable@...r.kernel.org> # v4.4+

---

Changes in v2:
- Hide the options behind CONFIG_DEBUG_KERNEL.

 arch/mips/Kconfig.debug | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index f0e314c..ee3dc9b 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -117,7 +117,16 @@ if CPU_MIPSR6
 
 choice
 	prompt "Compact branch policy"
-	default MIPS_COMPACT_BRANCHES_OPTIMAL
+	depends on DEBUG_KERNEL
+	default MIPS_COMPACT_BRANCHES_DEFAULT
+
+config MIPS_COMPACT_BRANCHES_DEFAULT
+	bool "Toolchain Default (don't specify)"
+	help
+	  Don't pass the -mcompact-branches flag to the compiler, allowing it
+	  to use its default (generally "optimal"). This is particularly
+	  useful for early R6-supporting toolchains which don't support the
+	  -mcompact-branches flag.
 
 config MIPS_COMPACT_BRANCHES_NEVER
 	bool "Never (force delay slot branches)"
-- 
2.8.2