[PATCH v2 2/2] riscv: Support DCACHE_WORD_ACCESS

[Chen Huang]

This patch selects DCACHE_WORD_ACCESS on riscv and implements support
for load_unaligned_zeropad.

DCACHE_WORD_ACCESS uses the word-at-a-time API for optimised string
comparisons in the vfs layer.

Signed-off-by: Chen Huang <chenhuang5@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 arch/riscv/Kconfig                      |  1 +
 arch/riscv/include/asm/word-at-a-time.h | 37 +++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index cd0be39d4c08..4e98ff76977f 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -44,6 +44,7 @@ config RISCV
 	select CLONE_BACKWARDS
 	select CLINT_TIMER if !MMU
 	select COMMON_CLK
+	select DCACHE_WORD_ACCESS if HAVE_EFFICIENT_UNALIGNED_ACCESS
 	select EDAC_SUPPORT
 	select GENERIC_ARCH_TOPOLOGY if SMP
 	select GENERIC_ATOMIC64 if !64BIT
diff --git a/arch/riscv/include/asm/word-at-a-time.h b/arch/riscv/include/asm/word-at-a-time.h
index 7c086ac6ecd4..8f4ad1ec39fb 100644
--- a/arch/riscv/include/asm/word-at-a-time.h
+++ b/arch/riscv/include/asm/word-at-a-time.h
@@ -45,4 +45,41 @@ static inline unsigned long find_zero(unsigned long mask)
 /* The mask we created is directly usable as a bytemask */
 #define zero_bytemask(mask) (mask)
 
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+#include <asm/asm.h>
+
+/*
+ * Load an unaligned word from kernel space.
+ *
+ * In the (very unlikely) case of the word being a page-crosser
+ * and the next page not being mapped, take the exception and
+ * return zeroes in the non-existing part.
+ */
+static inline unsigned long load_unaligned_zeropad(const void *addr)
+{
+	unsigned long ret, tmp;
+
+	/* Load word from unaligned pointer addr */
+	asm(
+	"1:	" REG_L " %0, %3\n"
+	"2:\n"
+	"	.section .fixup,\"ax\"\n"
+	"	.balign 2\n"
+	"3:	andi	%1, %2, ~0x7\n"
+	"	" REG_L " %0, (%1)\n"
+	"	andi	%1, %2, 0x7\n"
+	"	slli	%1, %1, 0x3\n"
+	"	srl	%0, %0, %1\n"
+	"	jump	2b, %1\n"
+	"	.previous\n"
+	"	.section __ex_table,\"a\"\n"
+	"	.balign	" RISCV_SZPTR "\n"
+	"	" RISCV_PTR "	1b, 3b\n"
+	"	.previous"
+	: "=&r" (ret), "=&r" (tmp)
+	: "r" (addr), "m" (*(unsigned long *)addr));
+
+	return ret;
+}
+#endif	/* DCACHE_WORD_ACCESS */
 #endif /* _ASM_RISCV_WORD_AT_A_TIME_H */
-- 
2.25.1