From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [PATCH] net:cpsw: Pass unhandled ioctl's on to generic phy ioctl Date: Wed, 5 Feb 2014 08:12:51 +0100 Message-ID: <20140205071250.GA4071@netboy> References: <1391500242-10554-1-git-send-email-stefan.sorensen@spectralink.com> <1391511050.3003.21.camel@deadeye.wl.decadent.org.uk> <1391526492.7871.8.camel@e37108.spectralink.com> <1391550719.3003.33.camel@deadeye.wl.decadent.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: =?iso-8859-1?B?U/hyZW5zZW4s?= Stefan , "davem@davemloft.net" , "netdev@vger.kernel.org" , "mugunthanvnm@ti.com" To: Ben Hutchings Return-path: Received: from mail-ea0-f179.google.com ([209.85.215.179]:36667 "EHLO mail-ea0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932072AbaBEHM4 (ORCPT ); Wed, 5 Feb 2014 02:12:56 -0500 Received: by mail-ea0-f179.google.com with SMTP id q10so939ead.10 for ; Tue, 04 Feb 2014 23:12:55 -0800 (PST) Content-Disposition: inline In-Reply-To: <1391550719.3003.33.camel@deadeye.wl.decadent.org.uk> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Feb 04, 2014 at 09:51:59PM +0000, Ben Hutchings wrote: > > Right. If all versions of CPSW include hardware timestamping then > bother with PHY timestamping at all? And why make CONFIG_TI_CPTS > configurable? On the one hand, PHY time stamping is more accurate and offers synchronization performance that is measurably better than MAC time stamping. On the other hand, when using a MAC the CPU usually has much more direct access to the clock (for example, direct register access or PCIe, versus MDIO). I once worked on a project in which it was planned to have both kinds of hardware in the design, in order to keep our options open in the face of fluid requirements. So I think you can expect to see such combinations in the wild, especially in the embedded area. We cannot reasonably support both types in the kernel at the same time, and so it makes sense to have compile time options in MAC drivers to disable time stamping. Thanks, Richard