Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751085AbaLEKZR (ORCPT ); Fri, 5 Dec 2014 05:25:17 -0500 Received: from down.free-electrons.com ([37.187.137.238]:53161 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750743AbaLEKZO (ORCPT ); Fri, 5 Dec 2014 05:25:14 -0500 Date: Fri, 5 Dec 2014 11:24:27 +0100 From: Maxime Ripard To: Alexandre Courbot Cc: Linus Walleij , Benoit Parrot , Pantelis Antoniou , Jiri Prchal , "linux-gpio@vger.kernel.org" , Linux Kernel Mailing List , "devicetree@vger.kernel.org" Subject: Re: [Patch v2 1/2] gpio: add GPIO hogging mechanism Message-ID: <20141205102427.GU30256@lukather> References: <1416527684-19017-1-git-send-email-bparrot@ti.com> <1416527684-19017-2-git-send-email-bparrot@ti.com> <20141201163639.GI25249@lukather> <20141202161227.GH30256@lukather> <20141204142741.GQ30256@lukather> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="UC+RhZhEc8lcmajv" 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 --UC+RhZhEc8lcmajv Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Dec 04, 2014 at 11:49:19PM +0900, Alexandre Courbot wrote: > On Thu, Dec 4, 2014 at 11:27 PM, Maxime Ripard > wrote: > > Hi, > > > > On Thu, Dec 04, 2014 at 11:15:38PM +0900, Alexandre Courbot wrote: > >> On Wed, Dec 3, 2014 at 1:12 AM, Maxime Ripard > >> wrote: > >> > On Tue, Dec 02, 2014 at 03:29:46PM +0100, Linus Walleij wrote: > >> >> On Tue, Dec 2, 2014 at 3:13 PM, Alexandre Courbot wrote: > >> >> > On Tue, Dec 2, 2014 at 1:36 AM, Maxime Ripard > >> >> > wrote: > >> >> > >> >> >> The only thing I'd like to have would be that the request here w= ould > >> >> >> be non-exclusive, so that a later driver would still be allowed = later > >> >> >> on to request that GPIO later on and manage it itself (ideally u= sing > >> >> >> the usual gpiod_request function). > >> >> > > >> >> > Actually we have a plan (and I have some code too) to allow multi= ple > >> >> > consumers per GPIO. Although like Benoit I wonder why you would w= ant > >> >> > to hog a GPIO and then request it properly later. Also, that prob= ably > >> >> > means we should abandon the hog since it actively drives the line= and > >> >> > would interfere with the late requested. How to do that correctly= is > >> >> > not really clear to me. > >> >> > >> >> I don't get the usecase. A hogged GPIO is per definition hogged. > >> >> This sounds more like "initial settings" or something, which is ano= ther > >> >> usecase altogether. > >> > > >> > We do have one board where we have a pin (let's say GPIO14 of the ba= nk > >> > A) that enables a regulator that will provide VCC the bank B. > >> > > >> > Now, both banks are handled by the same driver, but in order to have= a > >> > working output on the bank B, we do need to set GPIO14 as soon as > >> > we're probed. > >> > > >> > Just relying on the usual deferred probing introduces a circular > >> > dependency between the gpio-regulator that needs to grab its GPIO fr= om > >> > a driver not there yet, and the gpio driver that needs to enable its > >> > gpio-regulator. > >> > >> I don't get it. According to what you said, the following order should > >> go through IIUC: > >> > >> 1) bank A is probed, gpio 14 is available > >> 2) gpio-regulator is probed, acquires GPIO 14, regulator for Bank B is= available > >> 3) bank B is probed, grabs its regulator and turn it on, probes. > >> > >> What am I missing? > > > > It would be true if bank A and B were exposed through different > > drivers (or at least different instances of the same driver), which is > > not the case. > > > > In our case, banks A and B are handled by the same instance. >=20 > Ok, so both banks A and B are part of the same device/DT node. Now I > think I understand the issue. You need to hog the pin so that bank B > will work right after the device is probed. Exactly. > But you will still have the problem that the regulator device will > *not* be available when your device is probed, so you cannot call > regulator_get() for bank B anyway. I guess your only choice is to hog > that pin and leave it active ad vitam eternam. Hmmm, indeed. I'll stop boring you with this then :) Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com --UC+RhZhEc8lcmajv Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUgYfbAAoJEBx+YmzsjxAgmpsP/R3WiGc4Ttc7NDAtwfbgkOo2 OPWrvJ4xE6vJn+kEzD4Ku3MVvW7AZdJXB5pQjYsUp0upEWVfIf8K3OL3hAW9qcg8 rn7HQJZube7cTbMuR4MR4+pyJmjyWyRAeHKtEdNu/VeOYGQDzFeCCINQElE7EjmL BAe7fr0cZfdJgXxOFibAUWFHF+4ADRE0ApOj+MnIzf0PiDCiziAqmtxI6tZxNB3g Zbz83pDrzui2+NCnP+qAMluCEDn82Wb0GCbC3CH1k33Q/wzX0uR5SyRpULfdrZWe nZW2c0CxcAFElpAol1r+89JpKdyF7M0bBcLnVAGy2+jchdrTDPQ/gLZvh5/7L5+2 GqE7NTuTqTO6iJlIccI9+dnYprrDuD2oIdnywp6NVpswYGSVEZntMhqKLzlptj9z UIN4HIeCbzNy8057GErgNJL8rBrAXn5ThfF+ADCrSWKkA2G+KVrexQEQgVN34jwB rPILYBihRjSz03s1b22uNJZpUt0+vgdU9O3k7oKPz+KSD0YM2Yqxrj3uEqNYfJia K+0c5WoLg7HLSxfbT73a/HqFxYVX9QlbQiAlPkol9YtHne6lqz3s6eacc3KmfjKd i09bbdbw/6TtiqE8G2w0QsCvdgsKkNpo8k+etXSzI2mW+rYu52WISMMhp/klZkOi r/gLhjZoZ65iAiCaN4Z1 =3zZ9 -----END PGP SIGNATURE----- --UC+RhZhEc8lcmajv-- -- 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/