[PATCH v2 03/10] riscv: Implement cmpxchg8/16() using Zabha

Alexandre Ghiti
2024-06-26T13:06:57Z

This adds runtime support for Zabha in cmpxchg8/16() operations.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
arch/riscv/Kconfig | 17 ++++++++++++++++
arch/riscv/Makefile | 3 +++
arch/riscv/include/asm/cmpxchg.h | 34 ++++++++++++++++++++++++++++++--
3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1caaedec88c7..d3b0f92f92da 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -596,6 +596,23 @@ config RISCV_ISA_V_PREEMPTIVE
preemption. Enabling this config will result in higher memory
consumption due to the allocation of per-task's kernel Vector context.

+config TOOLCHAIN_HAS_ZABHA
+ bool
+ default y
+ depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zabha)
+ depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zabha)
+ depends on AS_HAS_OPTION_ARCH
+
+config RISCV_ISA_ZABHA
+ bool "Zabha extension support for atomic byte/halfword operations"
+ depends on TOOLCHAIN_HAS_ZABHA
+ default y
+ help
+ Enable the use of the Zabha ISA-extension to implement kernel
+ byte/halfword atomic memory operations when it is detected at boot.
+
+ If you don't know what to do here, say Y.
+
config TOOLCHAIN_HAS_ZACAS
bool
default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 9fd13d7a9cc6..78dcaaeebf4e 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -88,6 +88,9 @@ riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE) := $(riscv-march-y)_zihintpause
# Check if the toolchain supports Zacas
riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZACAS) := $(riscv-march-y)_zacas

+# Check if the toolchain supports Zabha
+riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZABHA) := $(riscv-march-y)_zabha
+
# Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by
# matching non-v and non-multi-letter extensions out with the filter ([^v_]*)
KBUILD_CFLAGS += -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index a58a2141c6d3..b9a3fdcec919 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -105,8 +105,20 @@
* indicated by comparing RETURN with OLD.
*/

-#define __arch_cmpxchg_masked(sc_sfx, prepend, append, r, p, o, n) \
+#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, prepend, append, r, p, o, n) \
({ \
+ __label__ no_zacas, zabha, end; \
+ \
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
+ asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
+ RISCV_ISA_EXT_ZACAS, 1) \
+ : : : : no_zacas); \
+ asm goto(ALTERNATIVE("nop", "j %[zabha]", 0, \
+ RISCV_ISA_EXT_ZABHA, 1) \
+ : : : : zabha); \
+ } \
+ \
+no_zacas:; \
u32 *__ptr32b = (u32 *)((ulong)(p) & ~0x3); \
ulong __s = ((ulong)(p) & (0x4 - sizeof(*p))) * BITS_PER_BYTE; \
ulong __mask = GENMASK(((sizeof(*p)) * BITS_PER_BYTE) - 1, 0) \
@@ -133,6 +145,19 @@
: "memory"); \
\
r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
+ goto end; \
+ \
+zabha: \
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
+ __asm__ __volatile__ ( \
+ prepend \
+ " amocas" cas_sfx " %0, %z2, %1\n" \
+ append \
+ : "+&r" (r), "+A" (*(p)) \
+ : "rJ" (n) \
+ : "memory"); \
+ } \
+end:; \
})

#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \
@@ -181,8 +206,13 @@ end:; \
\
switch (sizeof(*__ptr)) { \
case 1: \
+ __arch_cmpxchg_masked(sc_sfx, ".b" sc_sfx, \
+ prepend, append, \
+ __ret, __ptr, __old, __new); \
+ break; \
case 2: \
- __arch_cmpxchg_masked(sc_sfx, prepend, append, \
+ __arch_cmpxchg_masked(sc_sfx, ".h" sc_sfx, \
+ prepend, append, \
__ret, __ptr, __old, __new); \
break; \
case 4: \
--
2.39.2