From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH 01/10] xen/arm: vgic-v3: Correctly set
	GICD_TYPER.IDbits
Date: Tue, 20 Jan 2015 15:34:02 +0000
Message-ID: <1421768042.10440.292.camel@citrix.com>
References: <1421684957-29884-1-git-send-email-julien.grall@linaro.org>
	<1421684957-29884-2-git-send-email-julien.grall@linaro.org>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta4.messagelabs.com ([85.158.143.247])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <Ian.Campbell@citrix.com>) id 1YDb5C-0003WI-D9
	for xen-devel@lists.xenproject.org; Tue, 20 Jan 2015 15:51:10 +0000
In-Reply-To: <1421684957-29884-2-git-send-email-julien.grall@linaro.org>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Julien Grall <julien.grall@linaro.org>
Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com
List-Id: xen-devel@lists.xenproject.org

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.

Ian.