Re: [PATCH 1/2] target/riscv/cpu: set cpu->cfg in register_cpu_props()

[Alistair Francis]

On Wed, Jan 11, 2023 at 6:17 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> There is an informal contract between the cpu_init() functions and
> riscv_cpu_realize(): if cpu->env.misa_ext is zero, assume that the
> default settings were loaded via register_cpu_props() and do validations
> to set env.misa_ext.  If it's not zero, skip this whole process and
> assume that the board somehow did everything.
>
> At this moment, all SiFive CPUs are setting a non-zero misa_ext during
> their cpu_init() and skipping a good chunk of riscv_cpu_realize().
> This causes problems when the code being skipped in riscv_cpu_realize()
> contains fixes or assumptions that affects all CPUs, meaning that SiFive
> CPUs are missing out.
>
> To allow this code to not be skipped anymore, all the cpu->cfg.ext_* 
> attributes
> needs to be set during cpu_init() time. At this moment this is being done in
> register_cpu_props(). The SiFive oards are setting their own extensions during
> cpu_init() though, meaning that they don't want all the defaults from
> register_cpu_props().
>
> Let's move the contract between *_cpu_init() and riscv_cpu_realize() to
> register_cpu_props(). Inside this function we'll check if cpu->env.misa_ext
> was set and, if that's the case, set all relevant cpu->cfg.ext_*
> attributes, and only that. Leave the 'misa_ext' = 0 case as is today,
> i.e. loading all the defaults from riscv_cpu_extensions[].
>
> register_cpu_props() can then be called by all the cpu_init() functions,
> including the SiFive ones. This will make all CPUs behave more in line
> with that riscv_cpu_realize() expects.
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  target/riscv/cpu.h |  4 ++++
>  2 files changed, 44 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ee3659cc7e..b8c1edb7c2 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -262,6 +262,7 @@ static void rv64_sifive_u_cpu_init(Object *obj)
>  {
>      CPURISCVState *env = &RISCV_CPU(obj)->env;
>      set_misa(env, MXL_RV64, RVI | RVM | RVA | RVF | RVD | RVC | RVS | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_10_0);
>  }
>
> @@ -271,6 +272,7 @@ static void rv64_sifive_e_cpu_init(Object *obj)
>      RISCVCPU *cpu = RISCV_CPU(obj);
>
>      set_misa(env, MXL_RV64, RVI | RVM | RVA | RVC | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_10_0);
>      cpu->cfg.mmu = false;
>  }
> @@ -305,6 +307,7 @@ static void rv32_sifive_u_cpu_init(Object *obj)
>  {
>      CPURISCVState *env = &RISCV_CPU(obj)->env;
>      set_misa(env, MXL_RV32, RVI | RVM | RVA | RVF | RVD | RVC | RVS | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_10_0);
>  }
>
> @@ -314,6 +317,7 @@ static void rv32_sifive_e_cpu_init(Object *obj)
>      RISCVCPU *cpu = RISCV_CPU(obj);
>
>      set_misa(env, MXL_RV32, RVI | RVM | RVA | RVC | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_10_0);
>      cpu->cfg.mmu = false;
>  }
> @@ -324,6 +328,7 @@ static void rv32_ibex_cpu_init(Object *obj)
>      RISCVCPU *cpu = RISCV_CPU(obj);
>
>      set_misa(env, MXL_RV32, RVI | RVM | RVC | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_11_0);
>      cpu->cfg.mmu = false;
>      cpu->cfg.epmp = true;
> @@ -335,6 +340,7 @@ static void rv32_imafcu_nommu_cpu_init(Object *obj)
>      RISCVCPU *cpu = RISCV_CPU(obj);
>
>      set_misa(env, MXL_RV32, RVI | RVM | RVA | RVF | RVC | RVU);
> +    register_cpu_props(DEVICE(obj));
>      set_priv_version(env, PRIV_VERSION_1_10_0);
>      cpu->cfg.mmu = false;
>  }
> @@ -1139,10 +1145,44 @@ static Property riscv_cpu_extensions[] = {
>      DEFINE_PROP_END_OF_LIST(),
>  };
>
> +/*
> + * Register CPU props based on env.misa_ext. If a non-zero
> + * value was set, register only the required cpu->cfg.ext_*
> + * properties and leave. env.misa_ext = 0 means that we want
> + * all the default properties to be registered.
> + */
>  static void register_cpu_props(DeviceState *dev)
>  {
> +    RISCVCPU *cpu = RISCV_CPU(OBJECT(dev));
> +    uint32_t misa_ext = cpu->env.misa_ext;
>      Property *prop;
>
> +    /*
> +     * If misa_ext is not zero, set cfg properties now to
> +     * allow them to be read during riscv_cpu_realize()
> +     * later on.
> +     */
> +    if (cpu->env.misa_ext != 0) {
> +        cpu->cfg.ext_i = misa_ext & RVI;
> +        cpu->cfg.ext_e = misa_ext & RVE;
> +        cpu->cfg.ext_m = misa_ext & RVM;
> +        cpu->cfg.ext_a = misa_ext & RVA;
> +        cpu->cfg.ext_f = misa_ext & RVF;
> +        cpu->cfg.ext_d = misa_ext & RVD;
> +        cpu->cfg.ext_v = misa_ext & RVV;
> +        cpu->cfg.ext_c = misa_ext & RVC;
> +        cpu->cfg.ext_s = misa_ext & RVS;
> +        cpu->cfg.ext_u = misa_ext & RVU;
> +        cpu->cfg.ext_h = misa_ext & RVH;
> +        cpu->cfg.ext_j = misa_ext & RVJ;
> +
> +        /*
> +         * We don't want to set the default riscv_cpu_extensions
> +         * in this case.
> +         */
> +        return;
> +    }
> +
>      for (prop = riscv_cpu_extensions; prop && prop->name; prop++) {
>          qdev_property_add_static(dev, prop);
>      }
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 0158932dc5..798bd081de 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -63,6 +63,10 @@
>
>  #define RV(x) ((target_ulong)1 << (x - 'A'))
>
> +/*
> + * Consider updating register_cpu_props() when adding
> + * new MISA bits here.
> + */
>  #define RVI RV('I')
>  #define RVE RV('E') /* E and I are mutually exclusive */
>  #define RVM RV('M')
> --
> 2.39.0
>
>