ARM: lib64: Make string functions aware of MMU configuration

Optimized version of memset() in memset.S if called as:

    memset(foo, 0, size)

will try to explicitly zero out data cache with:

    dc	zva, dst

which will result in Alignement Exception (DABT) if MMU is not
enabled.

For more info see:

    - C4.4.8 "DC ZVA, Data Cache Zero by VA"
    - D5.2.8 "The effects of disabling a stage of address translation"

in "ARM Architecture Reference Manual. ARMv8, for ARMv8-A architecture
profile"

In similar vein, using optimized version of memcpy() could lead to a
unaligned 16-byte write (using 'stp'), which is not allowed for
Device-nGnRnE type of memory (see D5.2.8) and would liead to
Alignement Exception.

To fix both problems expose non-optimized and optimzied versions of
the function and created a wrapper to dispatch the call to either one
based on if MMU is enabled or not.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 37cde0c0c5..c6a4cadb32 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -353,6 +353,13 @@ menu "ARM specific settings"
 
 config ARM_OPTIMZED_STRING_FUNCTIONS
 	bool "use assembler optimized string functions"
+	#
+	# memset() and memcpy() in arm/lib64/mem[set|cpy].S are
+	# written with assumption of enabled MMU and cache. Depending
+	# on the inputs in may fail with Alignement exception if used
+	# without MMU
+	#
+	depends on !CPU_V8 || MMU
 	help
 	  Say yes here to use assembler optimized memcpy / memset functions.
 	  These functions work much faster than the normal versions but