From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934127AbeAXPmS (ORCPT ); Wed, 24 Jan 2018 10:42:18 -0500 Received: from mail-qt0-f169.google.com ([209.85.216.169]:39350 "EHLO mail-qt0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933953AbeAXPmQ (ORCPT ); Wed, 24 Jan 2018 10:42:16 -0500 X-Google-Smtp-Source: AH8x2260d8qj0LCt0HzFR07tnKmgn4lolUZDZXpoVGuOp/ARNnzq+BwkSjb4vnMsRjU5MrHJzKvjY1873k3R2e538rk= MIME-Version: 1.0 In-Reply-To: <20180124130705.GN3055@rfolt0960.corp.atmel.com> References: <20180115162407.6314-1-ludovic.desroches@microchip.com> <20180115162407.6314-3-ludovic.desroches@microchip.com> <20180118152228.GX2989@rfolt0960.corp.atmel.com> <20180124130705.GN3055@rfolt0960.corp.atmel.com> From: Andy Shevchenko Date: Wed, 24 Jan 2018 17:42:15 +0200 Message-ID: Subject: Re: [RFC PATCH 2/2] gpio: provide a consumer when requesting a gpio To: Linus Walleij , "open list:GPIO SUBSYSTEM" , Linux ARM , "linux-kernel@vger.kernel.org" , Nicolas Ferre Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 24, 2018 at 3:07 PM, Ludovic Desroches wrote: > On Thu, Jan 18, 2018 at 04:22:28PM +0100, Ludovic Desroches wrote: >> On Thu, Jan 18, 2018 at 11:30:00AM +0100, Linus Walleij wrote: >> > On Mon, Jan 15, 2018 at 5:24 PM, Ludovic Desroches >> > wrote: >> > I think we need to think over what is a good way to share ownership >> > of a pin. >> > >> > Russell pointed me to a similar problem incidentally and I briefly looked >> > into it: there are cases when several devices may need to hold the >> > same pin. >> > >> > Can't we just look up the associated gpio_chip from the GPIO range, >> > and in case the pin is connected between the pin controller and >> > the GPIO chip, then we allow the gpiochip to also take a >> > reference? How do you find my proposal about introducing ownership level (not requested yet; exclusive; shared)? >> It's the probably the way to go, it was Maxime's proposal and Andy seems >> to agree this solution. Confirm with caveat that this is a fix for subset of cases. > If pin_request() is called with gpio_range not NULL, it means that the > requests comes from a GPIO chip and the pin controller handles this pin. > In this case, I would say the pin is connected between the pin > controller and the GPIO chip. Is my assumption right? > > I am not sure it will fit all the cases: I think it doesn't cover cases when you have UART + UART + GPIO (I posted early a use case example). But at least it doesn't move things in a wrong direction. > - case 1: device A requests the pin (pinctrl-default state) and mux it > as a GPIO. Later,it requests the pin as a GPIO (gpiolib). This 'weird' > situation happens because some strict pin controllers were not declared > as strict and/or pinconf is needed. > > - case 2: device A requests the pin (pinctrl-default state). Device B > requests the pin as a GPIO (gpiolib). > > In case 1, pin_request must not return an error. In case 2, pin_request > must return an error even if the pin is connected between the pin > controller and the GPIO chip. For these cases looks OK to me. >> > I.e. in that case you just allow gpio_owner to proceed and take the >> > pin just like with a non-strict controller. -- With Best Regards, Andy Shevchenko