From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754177AbcDSNHS (ORCPT <rfc822;w@1wt.eu>);
	Tue, 19 Apr 2016 09:07:18 -0400
Received: from mail-wm0-f42.google.com ([74.125.82.42]:37672 "EHLO
	mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752861AbcDSNHP (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 19 Apr 2016 09:07:15 -0400
Date: Tue, 19 Apr 2016 15:07:08 +0200
From: Richard Cochran <richardcochran@gmail.com>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Shannon Nelson <shannon.nelson@intel.com>,
        Carolyn Wyborny <carolyn.wyborny@intel.com>,
        Don Skidmore <donald.c.skidmore@intel.com>,
        Bruce Allan <bruce.w.allan@intel.com>,
        John Ronciak <john.ronciak@intel.com>,
        Mitch Williams <mitch.a.williams@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: e1000e: can TIMINCA register be zero?
Message-ID: <20160419130708.GA7514@localhost.localdomain>
References: <57160BF8.6020001@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <57160BF8.6020001@redhat.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Apr 19, 2016 at 12:44:08PM +0200, Denys Vlasenko wrote:
> User says it happens on hotplug.

This sounds familiar.

   http://lists.openwall.net/netdev/2016/02/07/90

It also only ever happends in a VM, right?

> In 1000e_config_hwtstamp(), it is initialized before timecounter_init():

...

> By code inspection, e1000e_get_base_timinca() either returns -EINVAL
> and we don't do timecounter_init() and the division/0 location
> is not reached, or e1000e_get_base_timinca(&regval) sets
> nonzero regval. Then we set TIMINCA to this nonzero value.

Right, the register is always set to a non-zero value.
 
> Isn't it fishy that then timecounter_init() -> e1000e_cyclecounter_read()
> -> er32(TIMINCA) sees zero there?

Sure is.

Thanks,
Richard