From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F797C3F2D1 for ; Mon, 2 Mar 2020 16:44:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6057F2173E for ; Mon, 2 Mar 2020 16:44:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="BEMadxDu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726621AbgCBQov (ORCPT ); Mon, 2 Mar 2020 11:44:51 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:49264 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726451AbgCBQou (ORCPT ); Mon, 2 Mar 2020 11:44:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Db4N5RoeZpBqkyfQn2cjA7DvkkRvJVrKvDaxzHmGOoQ=; b=BEMadxDuaUoFQKUjh4nNDeXTt fonqrpNwJvY8x3p+/lIadBjI70zp3S+eUkrYMqBSYJqZzk0REK6OBxWBjTHq1le0auuHr4maSFkLG sejqg/06OQthx7bHf+N93wHyEz+rhteHPt1AgTC9eRzjJAWjLQwCXTp3qVawHMfNOiwbPSvkWqwMx 9BVeuNKNe44SAsHJjJcVOqvI/yvj9+YrQqwr5pqsr8qKGx70P5lPPeZSWs5of82p0PnhZMv8PYjTQ WlYWEmxvRMT+QYtCOMM/DGTehaUXist1iRwB8mGV1oJX16E+xRNvcbAfI23qMAp7ozQBO8OPD2QdJ Y6+EmQJng==; Received: from shell.armlinux.org.uk ([2001:4d48:ad52:3201:5054:ff:fe00:4ec]:47796) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1j8oBR-0002XR-Fc; Mon, 02 Mar 2020 16:44:45 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1j8oBP-000544-FV; Mon, 02 Mar 2020 16:44:43 +0000 Date: Mon, 2 Mar 2020 16:44:43 +0000 From: Russell King - ARM Linux admin To: Linus Walleij Cc: Alexandre Belloni , Linux GPIO List , Ludovic Desroches , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Romain Izard , Linux ARM Subject: Re: GPIOs not correctly exported via sysfs on ATSAMA5D2 Message-ID: <20200302164443.GI25745@shell.armlinux.org.uk> References: <20200302083959.wju5vz3acuka2edq@pengutronix.de> <20200302093607.GG25745@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Mon, Mar 02, 2020 at 05:34:19PM +0100, Linus Walleij wrote: > On Mon, Mar 2, 2020 at 10:36 AM Russell King - ARM Linux admin > wrote: > > On Mon, Mar 02, 2020 at 09:39:59AM +0100, Uwe Kleine-König wrote: > > > > - Sometimes it is useful to make use of a GPIO and a dedicated function > > > on the same pin in a driver (e.g. an i2c driver might need to switch > > > to gpio to do a bus recovery). The automatic pinmuxing then has > > > strange side effect because you have to remux the pins after > > > requesting the GPIOs even if you didn't drive the pins as GPIO and > > > there is a short time where the pin function isn't the dedicated > > > one. > > > > It's worse than that for the i2c driver. The pins are muxed to the i2c > > function when the driver binds. When the i2c driver claims the GPIOs > > corresponding with those pins, they get switched to GPIO mode behind > > the back of pinctrl. You then have to _explicitly_ switch pinctrl to > > GPIO mode and back to I2C mode to get them back to I2C mode. > > That's especially annoying. I would consider adding a specific > consumer flag for GPIOs used this way, in additon to > GPIOD_ASIS, something like GPIOD_ASIS_NOMUX > (thinking of better names). It's very annoying, and I believe something I did point out in my email about it when I discovered it towards the end of last year. Having a way to avoid the muxing would be a very good idea, as there are cases where we really should not be taking the I2C pins away from the controller during driver initialisation. In the case of i2c-pxa, when the pins are taken away, the controller sees the disconnected SCL and SDA lines go low, and it can assume that the bus is busy as a result, or worse see it as a START condition if SDA goes low while SCL is high. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up