On Mon, Dec 18, 2023 at 10:56 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> 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 <dbarboza@ventanamicro.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Alistair
> ---
> target/riscv/cpu-qom.h | 2 ++
> target/riscv/cpu.c | 46 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 48 insertions(+)
>
> diff --git a/target/riscv/cpu-qom.h b/target/riscv/cpu-qom.h
> index ca7dd509e3..4d1aa54311 100644
> --- a/target/riscv/cpu-qom.h
> +++ b/target/riscv/cpu-qom.h
> @@ -24,6 +24,7 @@
> #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)
> @@ -33,6 +34,7 @@
> #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 bb91bcacee..34102f6869 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -370,6 +370,17 @@ static void set_satp_mode_max_supported(RISCVCPU *cpu,
> /* Set the satp mode to the max supported */
> static void set_satp_mode_default_map(RISCVCPU *cpu)
> {
> + /*
> + * Bare CPUs do not default to the max available.
> + * Users must set a valid satp_mode in the command
> + * line.
> + */
> + if (object_dynamic_cast(OBJECT(cpu), TYPE_RISCV_BARE_CPU) != NULL) {
> + warn_report("No satp mode set. Defaulting to 'bare'");
> + cpu->cfg.satp_mode.map = (1 << VM_1_10_MBARE);
> + return;
> + }
> +
> cpu->cfg.satp_mode.map = cpu->cfg.satp_mode.supported;
> }
> #endif
> @@ -552,6 +563,28 @@ 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;
> +
> + /* Set to QEMU's first supported priv version */
> + env->priv_ver = PRIV_VERSION_1_10_0;
> +
> + /*
> + * Support all available satp_mode settings. The default
> + * value will be set to MBARE if the user doesn't set
> + * satp_mode manually (see set_satp_mode_default()).
> + */
> +#ifndef CONFIG_USER_ONLY
> + set_satp_mode_max_supported(RISCV_CPU(obj), VM_1_10_SV64);
> +#endif
> +}
> #else
> static void rv32_base_cpu_init(Object *obj)
> {
> @@ -1785,6 +1818,13 @@ 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,
> @@ -1807,6 +1847,11 @@ 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)
> @@ -1823,6 +1868,7 @@ 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
> };
>
> --
> 2.43.0
>
>