Re: [PATCH 01/10] xen/arm: vgic-v3: Correctly set GICD_TYPER.IDbits

From: Julien Grall <julien.grall@linaro.org>
To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: xen-devel@lists.xenproject.org, tim@xen.org,
	stefano.stabellini@citrix.com
Subject: Re: [PATCH 01/10] xen/arm: vgic-v3: Correctly set GICD_TYPER.IDbits
Date: Tue, 20 Jan 2015 17:16:55 +0000	[thread overview]
Message-ID: <54BE8D87.7060500@linaro.org> (raw)
In-Reply-To: <1421768042.10440.292.camel@citrix.com>

Hi Ian,

On 20/01/15 15:34, Ian Campbell wrote:
> On Mon, 2015-01-19 at 16:29 +0000, Julien Grall wrote:
>> +        unsigned int order;
>> +
>>          if ( dabt.size != DABT_WORD ) goto bad_width;
>>          /* No secure world support for guests. */
>>          *r = (((v->domain->max_vcpus << 5) & GICD_TYPE_CPUS ) |
>>                ((v->domain->arch.vgic.nr_lines / 32) & GICD_TYPE_LINES));
>> +
>> +        /*
>> +         * Calculate number of interrupt identifier bits supported by
>> +         * the GIC Stream Protocol Interface
>> +         */
>> +        irqs--;
>> +        for ( order = 0; irqs; order++ )
>> +            irqs >>= 1;
> 
> This is some variant on fls(). See get_bitmask_order() or
> get_count_order() for an example of use, possibly even one you could
> call.

get_count_order sounds the best function to use. I will give a try.

Regards,

-- 
Julien Grall