From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [Patch 2/4] x86/hpet: Sanitise HPET ACPI table and
 warn about multiple tables
Date: Mon, 7 Oct 2013 14:55:10 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, Keir Fraser <keir@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 07/10/13 14:45, Jan Beulich wrote:
>>>> On 07.10.13 at 15:26, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> --- a/xen/arch/x86/acpi/boot.c
>> +++ b/xen/arch/x86/acpi/boot.c
>> @@ -276,6 +276,21 @@ static int __init acpi_parse_hpet(struct 
>> acpi_table_header *table)
>>  		return -1;
>>  	}
>>  
>> +	if ( !hpet_tbl->address.address || !(hpet_tbl->address.address + 1) )
>> +	{
>> +		printk(KERN_WARNING PREFIX "Bad HPET address %#lx\n",
>> +		       hpet_tbl->address.address);
>> +		return -1;
>> +	}
> Did you really encounter a system where this would trigger?
>
>> +
>> +	/*
>> +	 * Hopefully someone might implement multiple HPET support in Xen.
>> +	 * Until then, warn the user if multiple HPET tables are found.
>> +	 */
>> +	if ( hpet_address )
>> +		printk(KERN_WARNING PREFIX
>> +		       "Xen only supports one HPET - Using latest table\n");
>> +
> You perhaps miunderstood how multiple HPETs would be surfaced
> by firmware: Not via multiple HPET tables, but via objects in the
> ACPI object namespace. With that, a similar question to the above
> arises: Have you seen a system where multiple HPET tables get
> surfaced?
>
> Jan
>

We had a system which had two HPET tables.  A BIOS update fixed the
issue, but the fact remains that in the case of multiple HPET tables, we
blindly go with the latest table.

Perhaps the message could change to "Multiple tables found (BIOS BUG?). 
Using information from latest" ?

~Andrew