From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from na01-bn1-obe.outbound.protection.outlook.com (mail-bn1on0147.outbound.protection.outlook.com [157.56.110.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 06D5B1A0C95 for ; Tue, 23 Dec 2014 08:26:06 +1100 (AEDT) Message-ID: <1419283551.5581.172.camel@freescale.com> Subject: Re: [PATCH] [v2] power/fsl: add MDIO dt binding for FMan From: Scott Wood To: Emil Medve Date: Mon, 22 Dec 2014 15:25:51 -0600 In-Reply-To: <5497FBAB.4010206@Freescale.com> References: <1415958800-9867-1-git-send-email-shh.xie@gmail.com> <1416966592.15957.172.camel@freescale.com> <1418940078.5581.143.camel@freescale.com> <1419030955.5581.154.camel@freescale.com> <5497D466.9090804@Freescale.com> <1419237176.5581.159.camel@freescale.com> <5497E645.7010500@Freescale.com> <1419241330.5581.162.camel@freescale.com> <5497FBAB.4010206@Freescale.com> Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Cc: "devicetree@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , Xie Shaohui-B21989 , Liberman Igal-B31950 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2014-12-22 at 05:08 -0600, Emil Medve wrote: > Hello Scott, > > > On 12/22/2014 03:42 AM, Scott Wood wrote: > > On Mon, 2014-12-22 at 03:37 -0600, Emil Medve wrote: > >> Hello Scott, > >> > >> > >> On 12/22/2014 02:32 AM, Scott Wood wrote: > >>> On Mon, 2014-12-22 at 02:20 -0600, Emil Medve wrote: > >>>> For the purpose of an example in the binding document, I suggest we just > >>>> stick with the IEEE standard frequency. > >>> > >>> The whole reason for this property existing in the device tree is > >>> non-standard frequencies. > >> > >> While the standard claims 2.5 MHz, most MDIO controllers and PHY devices > >> support frequencies well beyond the standard. Specifying a lower then > >> the standard frequency for the benefit of some errata is just one side > >> of this property > > > > The erratum was (until now) the only claimed reason for it. If there > > are other reasons why one would specify a different frequency (in > > particular, that relate to hardware description), please elaborate. > > From memory, the 1 Gb/s Vitesse PHY(s) we have on some of our DS boards > support 12.5 MHz. I can dig out more specs for specifics on other PHY(s) > > 2.5 MHz is slow and even more so for high speed interfaces. With both > polling and interrupts (both MDIO and/or PHY) we've noticed (or blamed) > in the past some Ethernet performance issues on this very slowness > > As of right now I'm not aware of another way to specify/coordinate the > MDC speed so setting a default (common denominator) in the DT that is > different then the IEEE standard seems ok > > >>>> We can continue this conversation about errata handling when we submit > >>>> the code relevant to this binding (and the FMan v3 support) > >>> > >>> It affects the binding, so let's discuss it now please. > >> > >> I think this specific (unpublished yet) errata has less bearing on the > >> binding then you might believe. This is mostly about providing a > >> common/default frequency supported by all the devices on some board > > > > What reason other than an erratum would there be for the standard > > frequency not being supported? > > This is not about not supporting the standard frequency. This is about > the default frequency being different then the standard OK, though rather than talk about defaults I'd phrase it as indicating that a higher frequency than standard is supported, or that a lower frequency than standard is required. -Scott