From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756791Ab1HXI4Z (ORCPT ); Wed, 24 Aug 2011 04:56:25 -0400 Received: from na3sys009aog115.obsmtp.com ([74.125.149.238]:40292 "EHLO na3sys009aog115.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756660Ab1HXI4U (ORCPT ); Wed, 24 Aug 2011 04:56:20 -0400 Date: Wed, 24 Aug 2011 11:56:16 +0300 From: Felipe Balbi To: Alan Stern Cc: Michal Nazarewicz , Felipe Balbi , Sebastian Andrzej Siewior , Yang Rui Rui , Dave Young , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv3 2/4] usb: gadget: replace "is_dualspeed" with "max_speed" Message-ID: <20110824085615.GD12549@legolas.emea.dhcp.ti.com> Reply-To: balbi@ti.com References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Ycz6tD7Th1CMF4v7" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Ycz6tD7Th1CMF4v7 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Tue, Aug 23, 2011 at 04:49:37PM -0400, Alan Stern wrote: > On Tue, 23 Aug 2011, Michal Nazarewicz wrote: >=20 > > On Tue, 23 Aug 2011 20:00:25 +0200, Alan Stern =20 > > wrote: > > > For the time being, perhaps the best answer is to use the _lowest_ > > > max_speed value among all the function drivers. It's the simplest > > > answer and most likely to be correct most of the time. > >=20 > > In theory, one could create a composite function with only SS/HS > > descriptors. >=20 > The only reason for doing that would be if the function was incapable > of carrying out its duties when running at full speed (insufficient > bandwidth, for example). Something like this is discussed briefly in=20 > section 9.2.6.6 of the USB-2 spec. >=20 > > So it would work for SS/HS but not for FS. I'm not > > saying that it would make sense (or that it's not a bug) but that > > adds to the discussion. >=20 > If somebody writes a composite gadget containing two functions, one of=20 > which supports only full speed and the other only high speed, they'll=20 > get what they deserve. :-) >=20 > Still, maybe I was wrong. Maybe it would be better to use the fastest > speed supported by at least one of the function drivers. The user can > always force a SuperSpeed-capable device to run at high speed by using > a USB-2 cable to plug it in. I'm not sure whether the user could force > such a device to run at full speed, however. plug it behind a full speed hub, like those that usually come on USB keyboards. --=20 balbi --Ycz6tD7Th1CMF4v7 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQEcBAEBAgAGBQJOVLyvAAoJEAv8Txj19kN13sQH/RlAMgL4LZsZBIX2MjkgJTn1 3pfpjS4A9KP9c1FFXOTlLEkwB/joeSDcCKXjMohLT6m3gmpUiPNx+bGboBmJAl9R sVTISnJQ6CPG6T0LCkRG5xJjdpCOeJYcHZHb7KajhrUAftWZ1uxqCqABjL7yuiVt nCpJg/3DSgKoexiGZiSMfS71HfP7ulIPDaDOPh+8glHmdM5sKekaSWWd7QXFSyb/ mkQNSRaVeTr22OdBbLtb5ZUURsdEyqY9gRWLwr/SRT4cZ8RYENk742F457ozniS9 oEivlSCzwrRndf1NU45HuO1OHw3mXBl+p5YsAuq8CJIk19/vtxux4UY+VCFofNM= =CC34 -----END PGP SIGNATURE----- --Ycz6tD7Th1CMF4v7--