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charset=us-ascii Content-Disposition: inline In-Reply-To: <20240717061957.140712-2-alexghiti@rivosinc.com> On Wed, Jul 17, 2024 at 08:19:47AM GMT, Alexandre Ghiti wrote: > This adds runtime support for Zacas in cmpxchg operations. > > Signed-off-by: Alexandre Ghiti > --- > arch/riscv/Kconfig | 17 +++++++++++++++++ > arch/riscv/Makefile | 3 +++ > arch/riscv/include/asm/cmpxchg.h | 26 +++++++++++++++++++++++--- > 3 files changed, 43 insertions(+), 3 deletions(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 05ccba8ca33a..1caaedec88c7 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_ZACAS > + bool > + default y > + depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zacas) > + depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zacas) > + depends on AS_HAS_OPTION_ARCH > + > +config RISCV_ISA_ZACAS > + bool "Zacas extension support for atomic CAS" > + depends on TOOLCHAIN_HAS_ZACAS > + default y > + help > + Enable the use of the Zacas ISA-extension to implement kernel atomic > + cmpxchg operations when it is detected at boot. > + > + If you don't know what to do here, say Y. > + > config TOOLCHAIN_HAS_ZBB > bool > default y > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 06de9d365088..9fd13d7a9cc6 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -85,6 +85,9 @@ endif > # Check if the toolchain supports Zihintpause extension > riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE) := $(riscv-march-y)_zihintpause > > +# Check if the toolchain supports Zacas > +riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZACAS) := $(riscv-march-y)_zacas > + > # Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by > # matching non-v and non-multi-letter extensions out with the filter ([^v_]*) > KBUILD_CFLAGS += -march=$(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 808b4c78462e..5d38153e2f13 100644 > --- a/arch/riscv/include/asm/cmpxchg.h > +++ b/arch/riscv/include/asm/cmpxchg.h > @@ -9,6 +9,7 @@ > #include > > #include > +#include > > #define __arch_xchg_masked(sc_sfx, prepend, append, r, p, n) \ > ({ \ > @@ -134,21 +135,40 @@ > r = (__typeof__(*(p)))((__retx & __mask) >> __s); \ > }) > > -#define __arch_cmpxchg(lr_sfx, sc_sfx, prepend, append, r, p, co, o, n) \ > +#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \ I'd either not bother renaming sc_sfx or also rename it in _arch_cmpxchg. > ({ \ > + __label__ no_zacas, end; \ > register unsigned int __rc; \ > \ > + if (IS_ENABLED(CONFIG_RISCV_ISA_ZACAS)) { \ > + asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \ > + RISCV_ISA_EXT_ZACAS, 1) \ > + : : : : no_zacas); \ > + \ > + __asm__ __volatile__ ( \ > + prepend \ > + " amocas" sc_cas_sfx " %0, %z2, %1\n" \ > + append \ > + : "+&r" (r), "+A" (*(p)) \ > + : "rJ" (n) \ > + : "memory"); \ > + goto end; \ > + } \ > + \ > +no_zacas: \ > __asm__ __volatile__ ( \ > prepend \ > "0: lr" lr_sfx " %0, %2\n" \ > " bne %0, %z3, 1f\n" \ > - " sc" sc_sfx " %1, %z4, %2\n" \ > + " sc" sc_cas_sfx " %1, %z4, %2\n" \ > " bnez %1, 0b\n" \ > append \ > "1:\n" \ > : "=&r" (r), "=&r" (__rc), "+A" (*(p)) \ > : "rJ" (co o), "rJ" (n) \ > : "memory"); \ > + \ > +end:; \ > }) > > #define _arch_cmpxchg(ptr, old, new, sc_sfx, prepend, append) \ > @@ -156,7 +176,7 @@ > __typeof__(ptr) __ptr = (ptr); \ > __typeof__(*(__ptr)) __old = (old); \ > __typeof__(*(__ptr)) __new = (new); \ > - __typeof__(*(__ptr)) __ret; \ > + __typeof__(*(__ptr)) __ret = (old); \ Is this just to silence some compiler warnings? Can we point out whatever the reason is in the commit message? > \ > switch (sizeof(*__ptr)) { \ > case 1: \ > -- > 2.39.2 > Thanks, drew