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=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E243CC433B4 for ; Sat, 24 Apr 2021 06:21:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0738613D8 for ; Sat, 24 Apr 2021 06:21:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229704AbhDXGWU (ORCPT ); Sat, 24 Apr 2021 02:22:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51594 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229702AbhDXGWP (ORCPT ); Sat, 24 Apr 2021 02:22:15 -0400 Received: from mail-pg1-x52f.google.com (mail-pg1-x52f.google.com [IPv6:2607:f8b0:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C96E5C061574 for ; Fri, 23 Apr 2021 23:21:37 -0700 (PDT) Received: by mail-pg1-x52f.google.com with SMTP id z16so36642543pga.1 for ; Fri, 23 Apr 2021 23:21:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=cKXei1xdQ+fu4f+TurzziSylf1siKskarIOy2DJy2qI=; b=PFyEeD0fM3AWJAq1JeqcNZ5c9R7IA8GwOxdpymg8IFAdzlLif3FxZ4qAKuKjJKEUDd wPMTx0+PTKmvEcgDB2o7p8CBpq2jzopKTruq0zavYWj9QnJwQmR0HURnDaWL2jEJ8laP F6kd8BvMvNgvsKIf4hoUxrCBY7ggU/dRFc/GlqNjYv3M9VhzueicSzGfqfDYkRM9o+Lj Px88M9JgQR/MIY2SPFno4LKCQmKOTNM/5MBUdvAUyxOAqYibpHS9t4dw/r1Fxx7rn+t4 foDdOT3v5PJE4MYA8o0mxCZzaRi/lBwkKr5Bef+wdXgxmjQ/ay6Mbkw86XU85Epo/0/W 9dbQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=cKXei1xdQ+fu4f+TurzziSylf1siKskarIOy2DJy2qI=; b=BXvkefYfbmv5vmXF9WV5xzvQsoOaRceJ9zIzYqziR3VeowSdAvMLiYl1bSG8yCd4cw SYf2qqwRJKZvdlXiUzM/M8Q2tIjrTFgLT5wvDXAkXzZEnGMGy99Mqi1HihZJ4nL1Ojvd dLXZ5kN4rZA1+hssOcETCOpzzWaMhWH6qBwv0X5l6cdAFEOLCxXeGRKsIwx6RkPhZSyb D0SbSYBgcC3/Du37LbEXKiz024q18kqHNGk90CJ+BgYMzgOzCdFye9h8SD/1q8xI4RVG Re1vpyI0DdDzb1IvTsuLfRRTqPzSfs6dhz8zej6mhnyGY6g8b84GRaVMSzlEs/j9hNAy MobQ== X-Gm-Message-State: AOAM531LAtWMzG4UhnqIyI08liwATekK9k7NHoyV6EYN6PPTrS4KkLmV knl9sPAkO71N/fhZv28tWFuyKKSYvcc= X-Google-Smtp-Source: ABdhPJz17kudDx0S84Jybdj2oyi98+9STMfOcnWEh6KylgVeQGDt+sY/6uHFF8GPKKFV6cb1nttrlA== X-Received: by 2002:a63:b09:: with SMTP id 9mr7204477pgl.107.1619245297339; Fri, 23 Apr 2021 23:21:37 -0700 (PDT) Received: from sol (106-69-187-97.dyn.iinet.net.au. [106.69.187.97]) by smtp.gmail.com with ESMTPSA id l18sm8654853pjq.33.2021.04.23.23.21.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Apr 2021 23:21:36 -0700 (PDT) Date: Sat, 24 Apr 2021 14:21:32 +0800 From: Kent Gibson To: Peter Rosin Cc: "linux-gpio@vger.kernel.org" Subject: Re: [libgpiod] Request an output line, without modifying the value Message-ID: <20210424062132.GA14885@sol> References: <6e26b4e5-277b-459f-29e7-7eb7e949e6a5@axentia.se> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e26b4e5-277b-459f-29e7-7eb7e949e6a5@axentia.se> Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Fri, Apr 23, 2021 at 05:32:15PM +0200, Peter Rosin wrote: > Hi! > > I'm wondering if there is a way to request an output line using > libgpiod without clobbering the previous value. I would like for > an application to take a peek at this previous value of an output > gpio and behave slightly different for 0/1. > > Cheers, > Peter Assuming it is still an output then GPIOD_LINE_REQUEST_DIRECTION_AS_IS should do what you are after. But there is no guarantee that the line state is preserved across requests, so YMMV. Cheers, Kent.