From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933221AbaGQOeO (ORCPT ); Thu, 17 Jul 2014 10:34:14 -0400 Received: from mail.active-venture.com ([67.228.131.205]:56459 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932361AbaGQOeN (ORCPT ); Thu, 17 Jul 2014 10:34:13 -0400 X-Originating-IP: 108.223.40.66 Message-ID: <53C7DEE3.6060107@roeck-us.net> Date: Thu, 17 Jul 2014 07:34:11 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Alexandre Courbot CC: "linux-gpio@vger.kernel.org" , Linux Kernel Mailing List , Linus Walleij Subject: Re: [PATCH] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one References: <1405552260-30511-1-git-send-email-linux@roeck-us.net> <53C76F3C.6090104@roeck-us.net> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/17/2014 12:26 AM, Alexandre Courbot wrote: > On Thu, Jul 17, 2014 at 3:37 PM, Guenter Roeck wrote: >> On 07/16/2014 11:09 PM, Alexandre Courbot wrote: >>> >>> On Thu, Jul 17, 2014 at 8:11 AM, Guenter Roeck wrote: >>>> >>>> The gpio include file and the gpio documentation declare and document >>>> GPIOF_ACTIVE_LOW as one of the flags to be passed to gpio_request_one >>>> and related functions. However, the flag is not evaluated or used. >>>> >>>> Check the flag in gpio_request_one and set the gpio internal flag >>>> FLAG_ACTIVE_LOW if it is set. >>> >>> >>> What is the point since the integer GPIO API has no clue of the >>> active-low status of a GPIO? It is only used by the gpiod and sysfs >>> interfaces. >>> >> >> One can use gpio_request_one() to export a gpio pin to user space from >> the kernel. That code path does use the flag, as you point out yourself >> above. > > Ok, in that case I suppose it makes sense. > > Reviewed-by: Alexandre Courbot > >> One could also argue that the integer gpio API _should_ support this as >> well, >> but that is a different question. > > Probably not going to happen. The integer GPIO interface is deprecated > and users who need new features should seriously consider switching to > gpiod. > The new API is unfortunately not equivalent to the old one. For example, if I understand correctly, gpiod_get is expected to be used instead of gpio_request_one. That may work nicely in a world with full DT or ACPI support, but doesn't work as well otherwise unless one drops the notion of using platform specific drivers built as modules (gpiod_add_lookup_table is not exported, and there is no remove function). Specifically, I don't see an easy way to convert mdio-gpio to use the new model, and that driver could really use support for an API which supports active-low pins. And even if gpiod_add_lookup_table was supported, converting a driver like this would be a major pain. Sure, it would be all easy if there would be a gpiod equivalent to gpio_request_one and gpio_request_array, but that is not the case. This makes converting drivers from the old to the new model challenging enough that I suspect that it won't really happen. Guenter