netdev - Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of the timecompare method

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Message-ID: <20120326152730.GA10212@localhost.localdomain>
Date:	Mon, 26 Mar 2012 17:27:30 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	chetan loke <loke.chetan@...il.com>
Cc:	"Keller, Jacob E" <jacob.e.keller@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH net V4 2/2] igb: offer a PTP Hardware Clock instead of
 the timecompare method

On Mon, Mar 26, 2012 at 11:07:40AM -0400, chetan loke wrote:
> On Sat, Mar 24, 2012 at 2:51 AM, Richard Cochran
> <richardcochran@...il.com> wrote:
> > On Fri, Mar 23, 2012 at 03:39:08PM -0400, chetan loke wrote:
> >>
> >> So, how is it working today? Because we could have tx and rx
> >> completions on different CPUs. Is it not possible to have the
> >> following race today - between timecompare_update->timecompare_offset
> >> -> timecounter_readdelta of say Rx and timecounter_cyc2time from Tx?
> >
> > I works (in the igb) because of the spinlock. You know, that thing
> > that you are so against using.
> >
> 
> I meant, was there a lock before the PHC functionality in igb?

There was no lock, and yes, it was a bug.

> >> How about rate limiting at the PHC class driver level? And then it
> >> will work across the board for all the adapters at the device level.
> >
> > No, don't go there. Enough bikeshedding already. If you have a serious
> 
> can a user without root privileges use get/adj/set time ioctls for the
> PHC functionality?

Depends on how you set the character device node permissions.

Thanks,
Richard
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