linux-kernel - Re: e1000e: can TIMINCA register be zero?

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Message-ID: <20160419130708.GA7514@localhost.localdomain>
Date:	Tue, 19 Apr 2016 15:07:08 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Shannon Nelson <shannon.nelson@...el.com>,
	Carolyn Wyborny <carolyn.wyborny@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	Mitch Williams <mitch.a.williams@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: e1000e: can TIMINCA register be zero?

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