From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752631AbeENIRB (ORCPT ); Mon, 14 May 2018 04:17:01 -0400 Received: from mail.bootlin.com ([62.4.15.54]:60961 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752332AbeENIMJ (ORCPT ); Mon, 14 May 2018 04:12:09 -0400 Date: Mon, 14 May 2018 10:11:51 +0200 From: Antoine Tenart To: Russell King - ARM Linux Cc: Antoine Tenart , davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, thomas.petazzoni@bootlin.com, maxime.chevallier@bootlin.com, gregory.clement@bootlin.com, miquel.raynal@bootlin.com, nadavh@marvell.com, stefanc@marvell.com, ymarkman@marvell.com, mw@semihalf.com Subject: Re: [PATCH net-next] net: phy: sfp: handle cases where neither BR,min nor BR,max is given Message-ID: <20180514081151.GD24660@kwain> References: <20180504152103.18152-1-antoine.tenart@bootlin.com> <20180508123026.GJ16141@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180508123026.GJ16141@n2100.armlinux.org.uk> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Russell, On Tue, May 08, 2018 at 01:30:26PM +0100, Russell King - ARM Linux wrote: > > The electronic engineer in me says that using zero isn't really valid > because there are coupling capacitors in the SFP module that block DC. > These blocking capacitors are required by the SFP+ specs to have a high > pass pole of between 20kHz and 100kHz - in other words, frequencies > below this are attenuated by the coupling capacitors. The relationship > between this and the bit rate will be a function of the encoding, so we > can't come to a definitive figure without some math (and I want to be > lazy about that!) > > Practically, we're talking about SerDes Ethernet, where the bit rate is > no lower than 100Mbps [*], which will always have a frequency well above > this cut-off. So, I don't have any problem with your approach to > setting the minimum to zero. Therefore, > > Acked-by: Russell King Thanks for looking into it! Antoine -- Antoine Ténart, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com