From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] x86/ACPI: allow CMOS RTC use even when ACPI
 says there is none
Date: Mon, 28 Jul 2014 14:46:09 +0100
Message-ID: <53D65421.6060305@citrix.com>
References: <53D28C91020000780002613E@mail.emea.novell.com>
	<53D644AF.8000801@citrix.com>
	<53D6627B02000078000269B3@mail.emea.novell.com>
	<53D64A7B.9080600@citrix.com>
	<53D66D020200007800026A2A@mail.emea.novell.com>
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.bemta5.messagelabs.com ([195.245.231.135])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <Andrew.Cooper3@citrix.com>) id 1XBlFn-0004tX-2P
	for xen-devel@lists.xenproject.org; Mon, 28 Jul 2014 13:46:15 +0000
In-Reply-To: <53D66D020200007800026A2A@mail.emea.novell.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: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 28/07/14 14:32, Jan Beulich wrote:
>>>> On 28.07.14 at 15:04, <andrew.cooper3@citrix.com> wrote:
>> On 28/07/14 13:47, Jan Beulich wrote:
>>>>> +
>>>>> +        start = NOW();
>>>>> +        do { /* must try at least 2.228 ms */
>>>>> +            t2 = NOW() - start;
>>>>> +        } while ( (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) &&
>>>>> +                  t2 < MILLISECS(3) );
>>>>> +
>>>>> +        __get_cmos_time(&rtc);
>>>>> +
>>>>> +        spin_unlock_irqrestore(&rtc_lock, flags);
>>>>> +
>>>>> +        if ( likely(!cmos_rtc_probe) ||
>>>>> +             t1 > SECONDS(1) || t2 >= MILLISECS(3) ||
>>>>> +             rtc.sec >= 60 || rtc.min >= 60 || rtc.hour >= 24 ||
>>>>> +             !rtc.day || rtc.day > 31 ||
>>>>> +             !rtc.mon || rtc.mon > 12 )
>>>>>              break;
>>>>> -    for ( i = 0 ; i < 1000000 ; i++ ) /* must try at least 2.228 ms */
>>>>> -        if ( !(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) )
>>>>> +
>>>>> +        if ( seconds < 60 )
>>>> Seconds doesn't appear to be updated before this point, meaning that we
>>>> will reprobe even if we find a plausible RTC.
>>> But that's exactly the point: We want to go through the loop twice.
>>> Only if the second round results in updated seconds do we consider
>>> the RTC okay for use.
>> Right, but in the case that the RTC is handing back static values (which
>> is slightly more likely if we are probing something which might not be a
>> CMOS RTC), we will sit in the loop forever.
> We won't: If seconds is an invalid value, we bail in the first iteration.
> If seconds is a valid value but unchanged on the second iteration,
> we bail there (see the still available context below.
>
> Jan

Silly me. I had mentally included the break in the if ( rtc.sec !=
seconds ) scope.

In which case, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Unfortunately we don't have affected hardware to test with.

~Andrew

>
>>>>> +        {
>>>>> +            if ( rtc.sec != seconds )
>>>>> +                cmos_rtc_probe = 0;
>>>>>              break;
>>>>> +        }
>>>>> +
>>>>> +        process_pending_softirqs();
>>>>> +
>>>>> +        seconds = rtc.sec;
>>>>> +    }
>>>>>  
>>>>> -    res = __get_cmos_time();
>>>>> +    if ( unlikely(cmos_rtc_probe) )
>>>>> +        panic("No CMOS RTC found - system must be booted from EFI");
>