Re: [PATCH] qemu/timer: Add host ticks function for RISC-V

[Richard Henderson <richard.henderson@linaro.org>]

On 9/7/23 20:23, LIU Zhiwei wrote:
> From: LIU Zhiwei <lzw194868@alibaba-inc.com>
> 
> Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
> ---
>   include/qemu/timer.h | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index 9a91cb1248..ce0b66d122 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -979,6 +979,25 @@ static inline int64_t cpu_get_host_ticks(void)
>       return cur - ofs;
>   }
>   
> +#elif defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen == 32
> +static inline int64_t cpu_get_host_ticks(void)
> +{
> +    uint32_t lo, hi;
> +    asm volatile("RDCYCLE %0\n\t"
> +                 "RDCYCLEH %1"
> +                 : "=r"(lo), "=r"(hi));
> +    return lo | (uint64_t)hi << 32;
> +}
> +
> +#elif defined(__riscv) && defined(__riscv_xlen) && __riscv_xlen > 32
> +static inline int64_t cpu_get_host_ticks(void)
> +{
> +    int64_t val;
> +
> +    asm volatile("RDCYCLE %0" : "=r"(cc));
> +    return val;
> +}

__riscv_xlen should never be undefined.

Don't you need a loop for RDCYCLEH to avoid time going backward?

     do {
         asm("rdcycleh %0\n\t"
             "rdcycle %1\n\t"
             "rdcycleh %2\n\t"
             : "=r"(hi), "=r"(lo), "=r"(tmph));
     } while (unlikely(tmph != hi));


r~