On Wed, Nov 01, 2023 at 06:27:02AM -0300, Daniel Henrique Barboza wrote: > > > On 11/1/23 06:02, Andrew Jones wrote: > > On Tue, Oct 31, 2023 at 05:39:03PM -0300, Daniel Henrique Barboza 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,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 | 25 +++++++++++++++++++++++++ > > > 2 files changed, 27 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 822970345c..98b2a4061a 100644 > > > --- a/target/riscv/cpu.c > > > +++ b/target/riscv/cpu.c > > > @@ -544,6 +544,18 @@ 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); > > > + > > > + /* Set latest version of privileged specification */ > > > + env->priv_ver = PRIV_VERSION_LATEST; > > > > The beauty of rv64i is we'll finally know exactly what we're configuring > > when we select it and some set of extensions. With that in mind I think > > we should also be explicit about which version of the priv spec is > > implemented, but we can't just pick a version now, since we may need to > > update it later. I think we have the following options: > > > > 1. Expose priv version properties (v1_10_0, ...) and either require the > > user to select one or default to the latest. (Any versions we don't > > want to support for rv64i would error out if selected.) > > This is already the case but it's a string property instead of booleans: > > $ ./build/qemu-system-riscv64 -M virt -cpu rv64i,priv_spec="v1.11.0" > $ ./build/qemu-system-riscv64 -M virt -cpu rv64i,priv_spec="v1.10.0" > $ ./build/qemu-system-riscv64 -M virt -cpu rv64i,priv_spec="not_valid" > qemu-system-riscv64: Unsupported privilege spec version 'not_valid' > > If users set 'priv_spec' we'll use it, otherwise rv64i will default to > 'latest'.
I think I'd prefer we don't have a default, but maybe in practice it'll be OK, since once we have S-mode profiles (which will most likely always be used with rv64i) then they'll override the default anyway. > > In case we do not want string values (and yeah, it's extra work to parse it, > check > if it's the right val and so on) then we can add priv spec bools that users > would > set on or off. We would need to deprecate "priv_spec" as it is. Yes, we should switch to booleans for cpu-model-expansion. I suppose we should keep the priv_ver default until we switch to booleans, though, in order to avoid encouraging more deprecated priv_spec usage in the meantime. > > This can be done outside of this work (we would need a RFC first probably). I can live with that. Thanks, drew