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Re: [PATCH v2] riscv: plic: Honour source priorities


From: Alistair Francis
Subject: Re: [PATCH v2] riscv: plic: Honour source priorities
Date: Fri, 19 Jun 2020 14:13:54 -0700

On Thu, Jun 18, 2020 at 1:24 PM Jessica Clarke <jrtc27@jrtc27.com> wrote:
>
> The source priorities can be used to order sources with respect to other
> sources, not just as a way to enable/disable them based off a threshold.
> We must therefore always claim the highest-priority source, rather than
> the first source we find.
>
> Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>

Thanks for the patch!

This looks good to me, I'll apply it to the RISC-V tree and it'll be
in my next round pull request.

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

Alistair

> ---
> Changes since v1:
>
>  * Initialise max_prio to plic->target_priority[addrid] rather than 0,
>    allowing the target priority comparison to be dropped and covered by
>    the max_prio comparison.
>
>  hw/riscv/sifive_plic.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/hw/riscv/sifive_plic.c b/hw/riscv/sifive_plic.c
> index 4f216c5585..d91e82b8ab 100644
> --- a/hw/riscv/sifive_plic.c
> +++ b/hw/riscv/sifive_plic.c
> @@ -166,6 +166,9 @@ static void sifive_plic_update(SiFivePLICState *plic)
>  static uint32_t sifive_plic_claim(SiFivePLICState *plic, uint32_t addrid)
>  {
>      int i, j;
> +    uint32_t max_irq = 0;
> +    uint32_t max_prio = plic->target_priority[addrid];
> +
>      for (i = 0; i < plic->bitfield_words; i++) {
>          uint32_t pending_enabled_not_claimed =
>              (plic->pending[i] & ~plic->claimed[i]) &
> @@ -177,14 +180,18 @@ static uint32_t sifive_plic_claim(SiFivePLICState 
> *plic, uint32_t addrid)
>              int irq = (i << 5) + j;
>              uint32_t prio = plic->source_priority[irq];
>              int enabled = pending_enabled_not_claimed & (1 << j);
> -            if (enabled && prio > plic->target_priority[addrid]) {
> -                sifive_plic_set_pending(plic, irq, false);
> -                sifive_plic_set_claimed(plic, irq, true);
> -                return irq;
> +            if (enabled && prio > max_prio) {
> +                max_irq = irq;
> +                max_prio = prio;
>              }
>          }
>      }
> -    return 0;
> +
> +    if (max_irq) {
> +        sifive_plic_set_pending(plic, max_irq, false);
> +        sifive_plic_set_claimed(plic, max_irq, true);
> +    }
> +    return max_irq;
>  }
>
>  static uint64_t sifive_plic_read(void *opaque, hwaddr addr, unsigned size)
> --
> 2.20.1
>
>



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