Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965481AbbEMTpI (ORCPT ); Wed, 13 May 2015 15:45:08 -0400 Received: from down.free-electrons.com ([37.187.137.238]:49718 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965064AbbEMTpF (ORCPT ); Wed, 13 May 2015 15:45:05 -0400 Date: Wed, 13 May 2015 21:41:06 +0200 From: Maxime Ripard To: Geert Uytterhoeven Cc: Mark Brown , Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , Hans de Goede , linux-spi , Martin Sperl , Michal Suchanek Subject: Re: [PATCH] spi: Force the registration of the spidev devices Message-ID: <20150513194106.GG4004@lukather> References: <1431462804-30467-1-git-send-email-maxime.ripard@free-electrons.com> <20150513112604.GI3066@sirena.org.uk> <20150513125102.GA2628@lukather> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="L+ofChggJdETEG3Y" Content-Disposition: inline In-Reply-To: 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 Content-Length: 2455 Lines: 64 --L+ofChggJdETEG3Y Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, May 13, 2015 at 09:10:48PM +0200, Geert Uytterhoeven wrote: > On Wed, May 13, 2015 at 2:51 PM, Maxime Ripard > wrote: > >> > This also adds an i2cdev-like feeling, where you get all the > >> > spidev devices all the time, without any modification. > >> > >> I2C is a bit safer here since it's a shared bus so you can't do > >> anything to devices not connected to the bus by mistake. > > > > I'm not sure to understand what you mean here. How is SPI different > > from that aspect? >=20 > If you talk to a nonexistent i2c device, nothing happens, as it just sends > a message with a nonexistent address on the shared bus. >=20 > If you talk to a nonexistent spi device, hell may break loose if e.g. some > "smart" hardware engineer used the "unused" CS as a pull-up for the > _RESET line on an external device... It's a bit like banging random > "unused" GPIOs. Ah, right. I'm always surprised by how creative the hardware engineers actually are :) Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --L+ofChggJdETEG3Y Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVU6jSAAoJEBx+YmzsjxAgESsQAIaSfvD6/CGHhYYyy/0tCK2C JNkmTYiEIgydq+9O3iHYqDFQWbxUtHrr3c9/co8S4xRLjTPAs3ghIEH6vO2AQ8Ov ctBWq2cnG36/ky4QZOaidjYlUjBGvEXveewSkDhaXuD1FSjiJDmFsEkC+kmRy7ds hdueiNqlWfJXeHHShc/OTDsaSBl8z6B5WwsTzxVIATjH6zItP8uIY2/JJMZvkWdb 4nuhgHQXgnOunq8wjdgwk4C1eRHHt8EVu76MEpKd5N6Df3eZN8dxC49TLPrem8Ov uZ+bInBzW9R3b61kP82ZrmxyDJCz4G5RSyp3YQCzfE6b6YhsnQrD5WzMg99/xDEV 3bdi1oZUeYThUKERg1gZFnKd7MqP/pZO7+IY095K3EnfPVvXxJvKb0QdI5ayJa4z MDJoMnIvpo+hM9mxJfW/oeGWzQ+gLxegijh+XlfzOYSPGnqsksI+Unm3QCjQd5Bd ALdgga2mWIVWshtNsFMi1kRKTFazCDpoPQRqQKeocZDUAthUrzVxuyGajSU12dp/ vb36XWYT8WlTsPXtg0o0YVNzLJR0W79kbEEEg2nxcRLSD6Uq+4f5x8JH4YWVJK4Z lvuM4l3Yd08uykXh0I8h0bamHXO4dpj+FHxfS9PbULXkxN0bZnwXWKqmBGcYylXt pVEdF9IdDwHqZqPKqfrN =zb6q -----END PGP SIGNATURE----- --L+ofChggJdETEG3Y-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/