Hi Yao, On 09:21 Sat 02 Aug , Yao Zi wrote: > Ratified on Apr. 2024, the original RISC-V "A" extension is now split > into two separate extensions, "Zaamo" for atomic operations and "Zalrsc" > for load-reserved/store-conditional instructions. > > For now, we've already seen real-world designs implement the Zalrsc > extension only[2]. As U-Boot mainly runs with only one HART, we could > easily support these designs by not using AMO instructions in the > hard-written assembly if necessary, for which this patch introduces two > new Kconfig options to indicate the availability of "Zaamo" and "Zalrsc". > > Note that even with this patch, "A" extension is specified in the ISA > string passed to the compiler as long as one of "Zaamo" or "Zalrsc" is > available, since they're only recognized with a quite recent version of > GCC/Clang. The compiler usually doesn't automatically generate atomic > instructions unless the source explicitly instructs it to do so, thus > this should be safe. > > Link: > https://github.com/riscv/riscv-zaamo-zalrsc/commit/d94c64c63e9120d56bdeb540caf2e5dae60a8126 > # [1] > Link: > https://lore.kernel.org/u-boot/20250729162035.209849-9-uros.sta...@htecgroup.com/ > # [2] > Signed-off-by: Yao Zi <zi...@disroot.org> > --- > arch/riscv/Kconfig | 17 +++++++++++++++++ > arch/riscv/Makefile | 7 ++++++- > configs/ibex-ast2700_defconfig | 3 ++- > 3 files changed, 25 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 8c6feae5735..b1c2d657e99 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -339,10 +339,27 @@ endmenu > > config RISCV_ISA_A > bool "Standard extension for Atomic Instructions" > + depends on RISCV_ISA_ZAAMO && RISCV_ISA_ZALRSC > default y > help > Adds "A" to the ISA string passed to the compiler. > > +config RISCV_ISA_ZAAMO > + bool "Standard extension for Atomic Memory Operations" > + default y > + help > + Indicates the platform supports Zaamo extension for atomic memory > + operations. Assembly routines won't use AMO instructions if set > + to n. > + > +config RISCV_ISA_ZALRSC > + bool "Standard extension for LR/SC instructions" > + default y > + help > + Indicates the platform supports Zalrsc extension for load-reserved > + and store-conditional instructions. Assembly rutines won't use s/rutines/routines/ while to be more precise, "Assembly routines" should be interpreted as instructions generated by compiler? if yes, can you improve the wording? > + LR/SC instructions if set to n. > + > config RISCV_ISA_ZICBOM > bool "Zicbom support" > depends on !SYS_DISABLE_DCACHE_OPS > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 6f80f4a7108..fdda6da1df3 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -11,7 +11,12 @@ ifeq ($(CONFIG_ARCH_RV32I),y) > ARCH_BASE = rv32im > ABI_BASE = ilp32 > endif > -ifeq ($(CONFIG_RISCV_ISA_A),y) > +# GCC starts to recognize "Zaamo" and "Zalrsc" from version 15, which is > quite > +# recent. We don't bother checking the exact compiler version, but pass "A" > +# extension for -march as long as one of "Zaamo" or "Zalrsc" is available. > +ifeq ($(findstring y,$(CONFIG_RISCV_ISA_A) \ > + $(CONFIG_RISCV_ISA_ZAAMO) \ > + $(CONFIG_RISCV_ISA_ZALRSC)),y) > ARCH_A = a > endif > ifeq ($(CONFIG_RISCV_ISA_F),y) > diff --git a/configs/ibex-ast2700_defconfig b/configs/ibex-ast2700_defconfig > index f088aec8716..eb5cab43645 100644 > --- a/configs/ibex-ast2700_defconfig > +++ b/configs/ibex-ast2700_defconfig > @@ -23,7 +23,8 @@ CONFIG_SYS_MEM_TOP_HIDE=0x10000000 > CONFIG_BUILD_TARGET="" > CONFIG_TARGET_ASPEED_AST2700_IBEX=y > # CONFIG_RISCV_ISA_F is not set > -# CONFIG_RISCV_ISA_A is not set > +# CONFIG_RISCV_ISA_ZAAMO is not set > +# CONFIG_RISCV_ISA_ZALRSC is not set > # CONFIG_SPL_SMP is not set > CONFIG_XIP=y > CONFIG_SPL_XIP=y > -- > 2.50.1 >
-- Yixun Lan (dlan)
