On 27.05.2025 13:30, Oleksii Kurochko wrote:
>
> On 5/26/25 8:44 PM, Oleksii Kurochko wrote:
>>>> + if ( !dt_property_read_u32(node, "riscv,guest-index-bits",
>>>> + &imsic_cfg.guest_index_bits) )
>>>> + imsic_cfg.guest_index_bits = 0;
>>>> + tmp = BITS_PER_LONG - IMSIC_MMIO_PAGE_SHIFT;
>>>> + if ( tmp < imsic_cfg.guest_index_bits )
>>>> + {
>>>> + printk(XENLOG_ERR "%s: guest index bits too big\n",
>>>> + dt_node_name(node));
>>>> + rc = -ENOENT;
>>>> + goto cleanup;
>>>> + }
>>>> +
>>>> + /* Find number of HART index bits */
>>>> + if ( !dt_property_read_u32(node, "riscv,hart-index-bits",
>>>> + &imsic_cfg.hart_index_bits) )
>>>> + {
>>>> + /* Assume default value */
>>>> + imsic_cfg.hart_index_bits = fls(*nr_parent_irqs);
>>>> + if ( BIT(imsic_cfg.hart_index_bits, UL) < *nr_parent_irqs )
>>>> + imsic_cfg.hart_index_bits++;
>>> Since fls() returns a 1-based bit number, isn't it rather that in the
>>> exact-power-of-2 case you'd need to subtract 1?
>> Agree, in this case, -1 should be taken into account.
>
> Hmm, it seems like in case of fls() returns a 1-based bit number there
> is not need for the check:
> (2) if ( BIT(imsic_cfg.hart_index_bits, UL) < *nr_parent_irqs )
>
> We could do imsic_cfg.hart_index_bits = fls(*nr_parent_irqs - 1) (1) without
> checking *nr_parent_irqs is power-of-two or not, and then just leave the
> check (2).
> And with (1), the check (2) is only needed for the case *nr_parent_irqs=1, if
> I amn't mistaken something. And if I'm not mistaken, then probably it make
> sense to change (2) to if ( *nr_parent_irqs == 1 ) + some comment why this
> case is so special.
>
> Does it make sense?
Can't easily tell; I'd like to see the resulting code instead of the textual
description.
Jan
