[U-Boot] [PATCH 1/2] arm: arm11: allow unaligned memory access

[Heinrich Schuchardt]

The UEFI spec mandates that unaligned memory access should be enabled if
supported by the CPU architecture.

This patch implements the function unaligned_access() to set the enable
unaligned data support flag and to clear the aligned flag in the system
control register (SCTLR). It is called when UEFI related commands like
bootefi are invoked.

Reported-by: Cristian Ciocaltea <cristian.ciocaltea at gmail.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
---
 arch/arm/cpu/arm11/Makefile |  4 ++++
 arch/arm/cpu/arm11/sctlr.S  | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 arch/arm/cpu/arm11/sctlr.S

diff --git a/arch/arm/cpu/arm11/Makefile b/arch/arm/cpu/arm11/Makefile
index 5d721fce12..5dfa01ae8d 100644
--- a/arch/arm/cpu/arm11/Makefile
+++ b/arch/arm/cpu/arm11/Makefile
@@ -4,3 +4,7 @@
 # Wolfgang Denk, DENX Software Engineering, wd at denx.de.

 obj-y	= cpu.o
+
+ifneq ($(CONFIG_SPL_BUILD),y)
+obj-$(CONFIG_EFI_LOADER) += sctlr.o
+endif
diff --git a/arch/arm/cpu/arm11/sctlr.S b/arch/arm/cpu/arm11/sctlr.S
new file mode 100644
index 0000000000..74a7fc4a25
--- /dev/null
+++ b/arch/arm/cpu/arm11/sctlr.S
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier:	GPL-2.0+ */
+/*
+ *  Routines to access the system control register
+ *
+ *  Copyright (c) 2019 Heinrich Schuchardt
+ */
+
+#include <linux/linkage.h>
+
+/*
+ * void allow_unaligned(void) - allow unaligned access
+ *
+ * This routine sets the enable unaligned data support flag and clears the
+ * aligned flag in the system control register.
+ * After calling this routine unaligned access does no longer leads to a
+ * data abort or undefined behavior but is handled by the CPU.
+ * For details see the "ARM Architecture Reference Manual" for ARMv6.
+ */
+ENTRY(allow_unaligned)
+	mrc	p15, 0, r0, c1, c0, 0	@ load system control register
+	orr	r0, r0, #1 << 22	@ set unaligned data support flag
+	bic	r0, r0, #2		@ clear aligned flag
+	mcr	p15, 0, r0, c1, c0, 0	@ write system control register
+	bx	lr			@ return
+ENDPROC(allow_unaligned)
--
2.24.0