From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Lunn Subject: Re: [PATCH net-next 06/19] net: usb: aqc111: Introduce link management Date: Mon, 8 Oct 2018 14:12:45 +0200 Message-ID: <20181008121245.GA6216@lunn.ch> References: <20181006173510.GE6990@lunn.ch> <9318605b-6ddc-a093-52ad-76c18097c414@aquantia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S . Miller" , "linux-usb@vger.kernel.org" , "netdev@vger.kernel.org" , Dmitry Bezrukov To: Igor Russkikh Return-path: Received: from vps0.lunn.ch ([185.16.172.187]:56938 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725857AbeJHTYO (ORCPT ); Mon, 8 Oct 2018 15:24:14 -0400 Content-Disposition: inline In-Reply-To: <9318605b-6ddc-a093-52ad-76c18097c414@aquantia.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Oct 08, 2018 at 09:29:26AM +0000, Igor Russkikh wrote: > Hi Andrew, > > >> aqc111_read_fw_version(dev, aqc111_data); > >> + aqc111_data->autoneg = AUTONEG_ENABLE; > >> + aqc111_data->advertised_speed = (usb_speed == USB_SPEED_SUPER) ? > >> + SPEED_5000 : SPEED_1000; > > > > > USB 3 has a raw bandwidth of 5Gbps. But it is a shared bus. So you > > have no guaranteed you are actually going to get the needed bandwidth > > to support line rate. > > > > USB 2.0 only gives you 480Mbps. So it won't even give you the full > > 1G. So using the same reasoning for USB3, maybe you should limit it to > > 100Mbps? > > > > I personally would not apply restrictions on the PHY depending on what > > USB is being used. > > First argument here is to reduce power consumption on USB2. > 2.5G/5G uses OCSGMII/XFI serdes which consumes more power. > Of course in normal conditions usb2 is capable to feed that, but > the risk still exists on legacy usb2 hardware. O.K, that sounds like a sensible argument. Please add a comment. I hope the Marketing Department also understand this. It should probably explain this on the product packaging. > > This becomes more important when using SFPs. If i have an SFP peer > > which is expecting 2500Base-X, but because the device is plugged into > > USB 2 port it is forced to use 1000Base-X, it is not going to get > > link. > > Do you mean here 2500Base-T? This particular device is an integrated > mac+phy, thus we can't easily link it with -X SFP endpoint. I only went to find the product brief after finishing the review. Without an external SERDES interface, SFP is not possible. But from your comment above, i does sound like internally it has such a SERDES. So it is not out of the question a follow up device is produced which could connect to an SFP. I actually have a no-name USB based SFP dongle... Andrew