Re: [PATCH -next v14 08/19] riscv: Introduce struct/helpers to save/restore per-task Vector state

Björn Töpel
2023-03-02T11:13:17Z

Andy Chiu <andy.chiu@sifive.com> writes:

> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
> index 692d3ee2d2d3..9c025f2efdc3 100644
> --- a/arch/riscv/include/asm/vector.h
> +++ b/arch/riscv/include/asm/vector.h
> @@ -31,11 +54,72 @@ static __always_inline void riscv_v_disable(void)
> csr_clear(CSR_SSTATUS, SR_VS);
> }
>
> +static __always_inline void __vstate_csr_save(struct __riscv_v_ext_state *dest)
> +{
> + asm volatile (
> + "csrr %0, " CSR_STR(CSR_VSTART) "\n\t"
> + "csrr %1, " CSR_STR(CSR_VTYPE) "\n\t"
> + "csrr %2, " CSR_STR(CSR_VL) "\n\t"
> + "csrr %3, " CSR_STR(CSR_VCSR) "\n\t"
> + : "=r" (dest->vstart), "=r" (dest->vtype), "=r" (dest->vl),
> + "=r" (dest->vcsr) : :);
> +}
> +
> +static __always_inline void __vstate_csr_restore(struct __riscv_v_ext_state *src)
> +{
> + asm volatile (
> + "vsetvl x0, %2, %1\n\t"
> + "csrw " CSR_STR(CSR_VSTART) ", %0\n\t"
> + "csrw " CSR_STR(CSR_VCSR) ", %3\n\t"
> + : : "r" (src->vstart), "r" (src->vtype), "r" (src->vl),
> + "r" (src->vcsr) :);
> +}
> +
> +static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to, void *datap)
> +{
> + riscv_v_enable();
> + __vstate_csr_save(save_to);
> + asm volatile (
> + "vsetvli t4, x0, e8, m8, ta, ma\n\t"
> + "vse8.v v0, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vse8.v v8, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vse8.v v16, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vse8.v v24, (%0)\n\t"
> + : : "r" (datap) : "t4", "memory");
> + riscv_v_disable();
> +}
> +
> +static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_from,
> + void *datap)
> +{
> + riscv_v_enable();
> + asm volatile (
> + "vsetvli t4, x0, e8, m8, ta, ma\n\t"
> + "vle8.v v0, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vle8.v v8, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vle8.v v16, (%0)\n\t"
> + "add %0, %0, t4\n\t"
> + "vle8.v v24, (%0)\n\t"
> + : : "r" (datap) : "t4");

Nit/question: For both enable/disable; Any reason to clobber t4, instead
of using a scratch reg?

Björn