Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756594Ab3IZKNm (ORCPT ); Thu, 26 Sep 2013 06:13:42 -0400 Received: from arroyo.ext.ti.com ([192.94.94.40]:36808 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755521Ab3IZKNl (ORCPT ); Thu, 26 Sep 2013 06:13:41 -0400 Message-ID: <524408BE.40402@ti.com> Date: Thu, 26 Sep 2013 13:13:18 +0300 From: Tomi Valkeinen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Mike Dunn , Thierry Reding CC: Richard Purdie , Jingoo Han , Jean-Christophe Plagniol-Villard , Grant Likely , Rob Herring , , , , , Robert Jarzmik , Marek Vasut Subject: Re: [PATCH] pwm-backlight: add support for device tree gpio control References: <1378236372-15711-1-git-send-email-mikedunn@newsguy.com> <20130910172130.GC22111@ulmo> <523056A6.5060000@newsguy.com> In-Reply-To: <523056A6.5060000@newsguy.com> X-Enigmail-Version: 1.5.2 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="NDDlI9o5jwvnxTdFENGHAnXjgNLGIg8Vv" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3344 Lines: 79 --NDDlI9o5jwvnxTdFENGHAnXjgNLGIg8Vv Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 11/09/13 14:40, Mike Dunn wrote: > On 09/10/2013 10:21 AM, Thierry Reding wrote: >> Do you have a real setup that actually needs multiple GPIOs? Usually >> such a setup requires some kind of timing or other additional constrai= nt >> which can't be represented by this simple binding. >> >> Looking at the Palm Treo code it seems like the reason why multiple >> GPIOs are needed is because one is to enable the backlight, while the >> other is in fact used to enable the LCD panel.=20 >=20 >=20 > There are actually four GPIOs involved! (There is an embarrasingly hor= rible > hack in arch/arm/mach-pxa/palmtreo.c that handles the others.) One is = almost > certainly simply backlight power. The other three are probably LCD rel= ated. When you say "power", do you mean the gpio enables a regulator to feed power to the backlight? If so, wouldn't that be a regulator, not gpio, from the bl driver's point of view? Generally speaking, this same problem appears in many places, but for some reason especially in display. I'm a bit hesitant in adding "free form" gpio/regulator support for drivers, as, as Thierry pointed out, there are often timing requirements, or sometimes the gpios are inverted, or sometimes the gpio is, in fact, a reset gpio, where you'll assert the gpio for a short moment only. I haven't seen new versions for the power sequences framework (without DT support), I think it could help us here a bit by simplifying how we present the sequences inside the driver. But we still need multiple drivers or the same driver supporting multiple devices. And I also think that the model where we have just one driver for, say, backlight may not be enough. There may be multiple hardware components, that used together will generate the backlight. And each component requires specific management. Tomi --NDDlI9o5jwvnxTdFENGHAnXjgNLGIg8Vv Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIcBAEBAgAGBQJSRAi+AAoJEPo9qoy8lh71yKgP/2Ru08KiKVeLi5TJ2a1T4yqH 6+541TbX0JlvQECfoEJjJ98eZ4eJWGrRwa9Soy3A5WA17CEvM8xk7XXIM/0G8FqE mMJbSoIX2ccwseuLMwbYTGuPAsWh9yqZLF7hdDZ3nQV2uET02JYcKBili4iK9vzG g2S3J1mrBQPKAKlj90Vyx8EgCOy/735c/oAaSIEF43PHYmao1E1dwChBXm2U86nr yFyeDOx6ApVs49jtHQAuXk9lwNccVR/yOP+BLCBQrLm+GD3A0bZApYsn0+YbNoaC UFsGiUw0IOByLrCqpDtfr7Z9XkZZT1jVgd+SijD4qIrjkHt/JohBGW4OX9KzaocH F27hKzUOaptGewXEtcv0ICYNUdB6O+6sa67O9ngp0+TfXELrhKoxAvwvSIfMTyhi WQo5H5BNZ+cW5WSFCfT0/4PXI/PGa+yB0f1U4TWBYz+lYq+cNl+juG7lpzOHRboT UFOkbIy9sf3vZVuo+/rmkZHM2WffNNxPxsbw4bGDeWxUZVWdGr+xMx4CgltjN2/c GiePDAH853QSogR/ha8emF2RUzYfTJxSW5rq61iCUxMrIqUE03IzQxaZA47Gm+iU W6OeKIdaD+osDOEi86RRlBYHX/LA8cPpty8bgWdSX1aVb0hXjW2OvZIahS1LwdOk ybLKvLfHHU908D4TVB+Q =OehU -----END PGP SIGNATURE----- --NDDlI9o5jwvnxTdFENGHAnXjgNLGIg8Vv-- -- 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/