Re: [Xen-devel] [PATCH v2] arm: clean-up: correct find_*_bit() functions use

[Julien Grall <julien.grall@xxxxxxx>]

Hi Artem,

Title: It would be good to specify the subsystem you modify.

arm: vgic: ...

On 24/05/18 16:24, Artem Mygaiev wrote:
> vgic_vcpu_pending_irq() uses find_next_bit() library function with 
> single 'unsigned long' variable, while it is designed to work with 
> memory regions and offsets. It would be more correct to use the 
> find_first_bit() function instead.
The commit message sounds like it is wrong to use find_next_bit(). 
However, as I mentioned earlier, find_first_bit() is just a wrapper of 
find_next_bit() on Arm64.
So I would reword the commit message as:

"arm: vgic: Use find_first_bit instead of find_next_bit when possible

find_next_bit(foo, sz, 0) is equivalent to find_first_bit(foo, sz). The 
latter is easier to understand. Some architecture may also have a 
optimized version of find_first_bit(...). So replace the occurrence of 
find_next_bit in vgic_vcpu_pending_irq()."
Cheers,

> Signed-off-by: Artem Mygaiev <artem_mygaiev@xxxxxxxx>
>
> diff --git a/xen/arch/arm/gic-vgic.c b/xen/arch/arm/gic-vgic.c
> index d831b35525..fd63906e9b 100644
> --- a/xen/arch/arm/gic-vgic.c
> +++ b/xen/arch/arm/gic-vgic.c
> @@ -362,7 +362,7 @@ int vgic_vcpu_pending_irq(struct vcpu *v)
>       ASSERT(v == current);
>
>       mask_priority = gic_hw_ops->read_vmcr_priority();
> -    active_priority = find_next_bit(&apr, 32, 0);
> +    active_priority = find_first_bit(&apr, 32);
>
>       spin_lock_irqsave(&v->arch.vgic.lock, flags);
--
Julien Grall

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