From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965219AbbEMTaI (ORCPT ); Wed, 13 May 2015 15:30:08 -0400 Received: from down.free-electrons.com ([37.187.137.238]:49368 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S964823AbbEMTaF (ORCPT ); Wed, 13 May 2015 15:30:05 -0400 Date: Wed, 13 May 2015 21:26:40 +0200 From: Maxime Ripard To: Greg Kroah-Hartman Cc: Mark Brown , linux-kernel@vger.kernel.org, Hans de Goede , linux-spi@vger.kernel.org, Martin Sperl , Michal Suchanek Subject: Re: [PATCH] spi: Force the registration of the spidev devices Message-ID: <20150513192640.GF4004@lukather> References: <1431462804-30467-1-git-send-email-maxime.ripard@free-electrons.com> <20150513112604.GI3066@sirena.org.uk> <20150513153740.GC11677@kroah.com> <20150513175034.GC4004@lukather> <20150513181736.GC16811@kroah.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="rWhLK7VZz0iBluhq" Content-Disposition: inline In-Reply-To: <20150513181736.GC16811@kroah.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --rWhLK7VZz0iBluhq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, May 13, 2015 at 11:17:36AM -0700, Greg Kroah-Hartman wrote: > On Wed, May 13, 2015 at 07:50:34PM +0200, Maxime Ripard wrote: > > Hi Greg, > >=20 > > On Wed, May 13, 2015 at 08:37:40AM -0700, Greg Kroah-Hartman wrote: > > > On Wed, May 13, 2015 at 12:26:04PM +0100, Mark Brown wrote: > > > > On Tue, May 12, 2015 at 10:33:24PM +0200, Maxime Ripard wrote: > > > >=20 > > > > > While this is nicer than the DT solution because of its accurate = hardware > > > > > representation, it's still not perfect because you might not have= access to the > > > > > DT, or you might be driving a completely generic device (such as a > > > > > microcontroller) that might be used for something else in a diffe= rent > > > > > context/board. > > > >=20 > > > > Greg, you're copied on this because this seems to be a generic prob= lem > > > > that should perhaps be solved at a driver model level - having a wa= y to > > > > bind userspace access to devices that we don't otherwise have a dri= ver > > > > for. The subsystem could specify the UIO driver to use when no oth= er > > > > driver is available. > > >=20 > > > That doesn't really work. I've been talking to the ACPI people about > > > this, and the problem is "don't otherwise have a driver for" is an > > > impossible thing to prove, as you never know when a driver is going to > > > be loaded from userspace. > > >=20 > > > You can easily bind drivers to devices today from userspace, why not > > > just use the built-in functionality you have today if you "know" that > > > there is no driver for this hardware. > >=20 > > What we're really after here is that we want to have an spidev > > instance when we don't even have a device. >=20 > That's crazy, just create a device, things do not work without one. Our use case is this one: we want to export spidev files so that "dev boards" with a header that allows to plug virtually anything on it (Raspberry Pi, Cubieboards, Xplained, and all the likes) without having to change the kernel and / or device tree. That would mean that if we plug something to that port, no device will be created because the DT itself won't have that device declared in the first place. This patch is actually doing this: creating a new device for all the chipselects that are not in use that will be bound to the spidev driver. Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --rWhLK7VZz0iBluhq Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVU6VwAAoJEBx+YmzsjxAgmmoP/iaEv0wDwdQYlibCwRkqDT83 +igaPKE2Ao3FFPvoi9XpHgwbVaxFLwbcmrMpdnvzq+/XuZUK/0JLVMfHvF/+CkmB DdbM/v54bH4VMj4na79swIgvK9r2xf3uhSJUXtiYU664Lmrj/4QkUQ66BAiZDaho ooFMsRb+kflYWgYb0sYEEWg4ynb38Fs9Nba6DKit0UkhbCTMjmx81tnwAWQH1pf+ XFd7T24p998WWCpsJmRBiEDd0leS2Psa60I2LFkh2Fwfh/gqz3s1kCCCvPeCXZvk 74uSlK98xMF+9VE3ntZnlX5Ory4d6tBwMhHbEX652A66m7pwu/6APH0u90Ke9qwO Z88Gx9HOQqZQzNnzzMJdqcr2JPcizyKo1MR6BtRPJl/GC6lAdQwtLhXh8wP093Um COw+zvF6TVN5fGP+XgMYUO5yBWQf/dxFGNZiDClP/UceaBi4+do+MvHGc5F1ckVa ctoc21PwwO9eePd4WSXbeWDocEqogF/T/bzC8UAGV6PQNfS5SNc5Lhq3pltvS0/a hZWbj7OD8Quwh/UESTHolIJZjHzIMTvXkTTZi/CcOCzkKFhNDTXXr7E3o9SX+RJj UxD0zvQdSpzqkwKb5yMVWjf3X11c0nFK+n7OcZc0wnrwpGyLJvj9GqJFYvoHLqz+ ixNy4FCl9w8Zytl3D1lD =ulER -----END PGP SIGNATURE----- --rWhLK7VZz0iBluhq--