From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH RFC 2/2] xen: arm: Enable physical address
 space compression (PDX) on arm64
Date: Thu, 07 Aug 2014 17:03:13 +0100
Message-ID: <53E3A341.2000502@linaro.org>
References: <a0063c96455a2512091f40df5b7b8ec5bbef4b13.1406804493.git.ian.campbell@citrix.com>
	<53da2211.8511ec0a.4375.46ddSMTPIN_ADDED_MISSING@mx.google.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
In-Reply-To: <53da2211.8511ec0a.4375.46ddSMTPIN_ADDED_MISSING@mx.google.com>
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: Ian Campbell <ian.campbell@citrix.com>, xen-devel@lists.xen.org
Cc: Roy Franz <roy.franz@linaro.org>, tim@xen.org, Fu Wei <fu.wei@linaro.org>, Jan Beulich <JBeulich@suse.com>, stefano.stabellini@eu.citrix.com
List-Id: xen-devel@lists.xenproject.org

Hi Ian,

On 07/31/2014 12:01 PM, Ian Campbell wrote:
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 446b4dc..dbd92bb 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -423,6 +423,46 @@ static paddr_t __init get_xen_paddr(void)
>      return paddr;
>  }
>  
> +/* Sets all bits from the most-significant 1-bit down to the LSB */
> +static u64 __init fill_mask(u64 mask)
> +{
> +    while (mask & (mask + 1))

Coding style: Missing spaces

> +        mask |= mask + 1;
> +    return mask;
> +}
> +
> +static void init_pdx(void)
> +{
> +    u64 mask = fill_mask(bootinfo.mem.bank[0].start - 1);
> +    int bank;
> +
> +    for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ )
> +    {
> +        paddr_t bank_start = bootinfo.mem.bank[bank].start;
> +        paddr_t bank_size = bootinfo.mem.bank[bank].size;
> +        paddr_t bank_end = bank_start + bank_size;
> +
> +        set_pdx_range(paddr_to_pfn(bank_start),
> +                      paddr_to_pfn(bank_end));
> +
> +
> +        mask |= bank_start | fill_mask(bank_start ^ (bank_end - 1));
> +    }
> +
> +    for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ )
> +    {
> +        paddr_t bank_start = bootinfo.mem.bank[bank].start;
> +        paddr_t bank_size = bootinfo.mem.bank[bank].size;
> +        paddr_t bank_end = bank_start + bank_size;
> +
> +        if (~mask &
> +            fill_mask(bank_start ^ (bank_end - 1)))

Coding style.

I don't really understand what the function is achieving. Could you
explain a bit more?

Regards,

-- 
Julien Grall