Re: [PATCH] target/riscv: Stop timer with infinite timecmp

[Alistair Francis]

On Thu, Aug 29, 2024 at 6:40 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> While the spec doesn't state it, setting timecmp to UINT64_MAX is
> another way to stop a timer, as it's considered setting the next
> timer event to occur at infinity. And, even if the time CSR does
> eventually reach UINT64_MAX, the very next tick will bring it back to
> zero, once again less than timecmp. For this reason
> riscv_timer_write_timecmp() special cases UINT64_MAX. However, if a
> previously set timecmp has not yet expired, then setting timecmp to
> UINT64_MAX to disable / stop it would not work, as the special case
> left the previous QEMU timer active, which would then still deliver
> an interrupt at that previous timecmp time. Ensure the stopped timer
> will not still deliver an interrupt by also deleting the QEMU timer
> in the UINT64_MAX special case.
>
> Fixes: ae0edf2188b3 ("target/riscv: No need to re-start QEMU timer when 
> timecmp == UINT64_MAX")
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>

Thanks!

Applied to riscv-to-apply.next

Alistair

> ---
>  target/riscv/time_helper.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/target/riscv/time_helper.c b/target/riscv/time_helper.c
> index 8d245bed3ae3..bc0d9a0c4c35 100644
> --- a/target/riscv/time_helper.c
> +++ b/target/riscv/time_helper.c
> @@ -92,6 +92,7 @@ void riscv_timer_write_timecmp(CPURISCVState *env, 
> QEMUTimer *timer,
>       * equals UINT64_MAX.
>       */
>      if (timecmp == UINT64_MAX) {
> +        timer_del(timer);
>          return;
>      }
>
> --
> 2.45.2
>
>