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Message-Id: <7ed390a0c72d9bba6a1ea5bdda92dde287b18fa0.1550692943.git.christophe.leroy@c-s.fr>
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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH v4 14/16] powerpc/kconfig: make _etext and data areas
 alignment configurable on Book3s 32
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, j.neuschaefer@gmx.net
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Thu, 21 Feb 2019 08:05:02 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Depending on the number of available BATs for mapping the different
kernel areas, it might be needed to increase the alignment of _etext
and/or of data areas.

This patchs allows the user to do it via Kconfig.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/Kconfig | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 26ddea487d72..127259179b4d 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -728,16 +728,44 @@ config THREAD_SHIFT
 	  Used to define the stack size. The default is almost always what you
 	  want. Only change this if you know what you are doing.
 
+config ETEXT_SHIFT_BOOL
+	bool "Set custom etext alignment" if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	depends on ADVANCED_OPTIONS
+	help
+	  This option allows you to set the kernel end of text alignment. When
+	  RAM is mapped by blocks, the alignment needs to fit the size and
+	  number of possible blocks. The default should be OK for most configs.
+
+	  Say N here unless you know what you are doing.
+
 config ETEXT_SHIFT
-	int
+	int "_etext shift" if ETEXT_SHIFT_BOOL
+	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
 	default 17 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
 	default PPC_PAGE_SHIFT
+	help
+	  On Book3S 32 (603+), IBATs are used to map kernel text.
+	  Smaller is the alignment, greater is the number of necessary IBATs.
+
+config DATA_SHIFT_BOOL
+	bool "Set custom data alignment" if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	depends on ADVANCED_OPTIONS
+	help
+	  This option allows you to set the kernel data alignment. When
+	  RAM is mapped by blocks, the alignment needs to fit the size and
+	  number of possible blocks. The default should be OK for most configs.
+
+	  Say N here unless you know what you are doing.
 
 config DATA_SHIFT
-	int
+	int "Data shift" if DATA_SHIFT_BOOL
 	default 24 if STRICT_KERNEL_RWX && PPC64
+	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
 	default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
 	default PPC_PAGE_SHIFT
+	help
+	  On Book3S 32 (603+), DBATs are used to map kernel text and rodata RO.
+	  Smaller is the alignment, greater is the number of necessary DBATs.
 
 config FORCE_MAX_ZONEORDER
 	int "Maximum zone order"
-- 
2.13.3