We don't have any form of a 'bare bones' CPU. rv64, our default CPUs, comes with a lot of defaults. This is fine for most regular uses but it's not suitable when more control of what is actually loaded in the CPU is required.
A bare-bones CPU would be annoying to deal with if not by profile support, a way to load a multitude of extensions with a single flag. Profile support is going to be implemented shortly, so let's add a CPU for it. The new 'rv64i' CPU will have only RVI loaded. It is inspired in the profile specification that dictates, for RVA22U64 [1]: "RVA22U64 Mandatory Base RV64I is the mandatory base ISA for RVA22U64" And so it seems that RV64I is the mandatory base ISA for all profiles listed in [1], making it an ideal CPU to use with profile support. rv64i is a CPU of type TYPE_RISCV_BARE_CPU. It has a mix of features from pre-existent CPUs: - it allows extensions to be enabled, like generic CPUs; - it will not inherit extension defaults, like vendor CPUs. This is the minimum extension set to boot OpenSBI and buildroot using rv64i: ./build/qemu-system-riscv64 -nographic -M virt \ -cpu rv64i,sv39=true,g=true,c=true,s=true,u=true Our minimal riscv,isa in this case will be: # cat /proc/device-tree/cpus/cpu@0/riscv,isa rv64imafdc_zicntr_zicsr_zifencei_zihpm_zca_zcd# [1] https://github.com/riscv/riscv-profiles/blob/main/profiles.adoc Signed-off-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com> --- target/riscv/cpu-qom.h | 2 ++ target/riscv/cpu.c | 23 +++++++++++++++++++++++ 2 files changed, 25 insertions(+) diff --git a/target/riscv/cpu-qom.h b/target/riscv/cpu-qom.h index 7831e86d37..ea9a752280 100644 --- a/target/riscv/cpu-qom.h +++ b/target/riscv/cpu-qom.h @@ -25,6 +25,7 @@ #define TYPE_RISCV_CPU "riscv-cpu" #define TYPE_RISCV_DYNAMIC_CPU "riscv-dynamic-cpu" #define TYPE_RISCV_VENDOR_CPU "riscv-vendor-cpu" +#define TYPE_RISCV_BARE_CPU "riscv-bare-cpu" #define RISCV_CPU_TYPE_SUFFIX "-" TYPE_RISCV_CPU #define RISCV_CPU_TYPE_NAME(name) (name RISCV_CPU_TYPE_SUFFIX) @@ -35,6 +36,7 @@ #define TYPE_RISCV_CPU_BASE32 RISCV_CPU_TYPE_NAME("rv32") #define TYPE_RISCV_CPU_BASE64 RISCV_CPU_TYPE_NAME("rv64") #define TYPE_RISCV_CPU_BASE128 RISCV_CPU_TYPE_NAME("x-rv128") +#define TYPE_RISCV_CPU_RV64I RISCV_CPU_TYPE_NAME("rv64i") #define TYPE_RISCV_CPU_IBEX RISCV_CPU_TYPE_NAME("lowrisc-ibex") #define TYPE_RISCV_CPU_SHAKTI_C RISCV_CPU_TYPE_NAME("shakti-c") #define TYPE_RISCV_CPU_SIFIVE_E31 RISCV_CPU_TYPE_NAME("sifive-e31") diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c index f7c1989d14..4a6e544eaf 100644 --- a/target/riscv/cpu.c +++ b/target/riscv/cpu.c @@ -544,6 +544,16 @@ static void rv128_base_cpu_init(Object *obj) set_satp_mode_max_supported(RISCV_CPU(obj), VM_1_10_SV57); #endif } + +static void rv64i_bare_cpu_init(Object *obj) +{ + CPURISCVState *env = &RISCV_CPU(obj)->env; + riscv_cpu_set_misa(env, MXL_RV64, RVI); + + /* Remove the defaults from the parent class */ + RISCV_CPU(obj)->cfg.ext_zicntr = false; + RISCV_CPU(obj)->cfg.ext_zihpm = false; +} #else static void rv32_base_cpu_init(Object *obj) { @@ -1753,6 +1763,13 @@ void riscv_cpu_list(void) .instance_init = initfn \ } +#define DEFINE_BARE_CPU(type_name, initfn) \ + { \ + .name = type_name, \ + .parent = TYPE_RISCV_BARE_CPU, \ + .instance_init = initfn \ + } + static const TypeInfo riscv_cpu_type_infos[] = { { .name = TYPE_RISCV_CPU, @@ -1775,6 +1792,11 @@ static const TypeInfo riscv_cpu_type_infos[] = { .parent = TYPE_RISCV_CPU, .abstract = true, }, + { + .name = TYPE_RISCV_BARE_CPU, + .parent = TYPE_RISCV_CPU, + .abstract = true, + }, DEFINE_DYNAMIC_CPU(TYPE_RISCV_CPU_ANY, riscv_any_cpu_init), DEFINE_DYNAMIC_CPU(TYPE_RISCV_CPU_MAX, riscv_max_cpu_init), #if defined(TARGET_RISCV32) @@ -1791,6 +1813,7 @@ static const TypeInfo riscv_cpu_type_infos[] = { DEFINE_VENDOR_CPU(TYPE_RISCV_CPU_THEAD_C906, rv64_thead_c906_cpu_init), DEFINE_VENDOR_CPU(TYPE_RISCV_CPU_VEYRON_V1, rv64_veyron_v1_cpu_init), DEFINE_DYNAMIC_CPU(TYPE_RISCV_CPU_BASE128, rv128_base_cpu_init), + DEFINE_BARE_CPU(TYPE_RISCV_CPU_RV64I, rv64i_bare_cpu_init), #endif }; -- 2.41.0