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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 DA3CAC12002 for ; Fri, 16 Jul 2021 08:24:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B90FB613E3 for ; Fri, 16 Jul 2021 08:24:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236794AbhGPI1D (ORCPT ); Fri, 16 Jul 2021 04:27:03 -0400 Received: from gofer.mess.org ([88.97.38.141]:34181 "EHLO gofer.mess.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231851AbhGPI1C (ORCPT ); Fri, 16 Jul 2021 04:27:02 -0400 Received: by gofer.mess.org (Postfix, from userid 1000) id 0894EC65B9; Fri, 16 Jul 2021 09:24:05 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mess.org; s=2020; t=1626423846; bh=k4GV0GyL3ss27o/H8GNejAFIH+XbYUndAcIjCC5L3s4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P3O4/mlSQPw+CSbX13SWksOS8UAwp1Lh+QLjaMXCjvYFKitLQQSNAqSO20WtJHPPe aiydCsjegm81mLgM84FLrRBk/hnymcloU1EUeRcRs+4s9fC3xB/x9sZuPk+JITlR1f J82igZN51I+16tN0UtumrXDfkbn9cAcU4bVqVgwS5N4KGz+uUDTJYRbhDIB8wfwOB6 DvnP4ABtNJ2ST682LTafKe4pQEMhtufXC831QFu3RwfHKc2/7aLYw4kOSl8PEqBE0U nzXZl42EpJRk7ZBW6FW/JJgu3z/UjKuWDR7VrehEP90Lco3uEqNTF9AJo1aSx/ozf2 WF3YnLyyzpzzA== Date: Fri, 16 Jul 2021 09:24:05 +0100 From: Sean Young To: Viktor Prutyanov Cc: mchehab@kernel.org, robh+dt@kernel.org, khilman@baylibre.com, narmstrong@baylibre.com, jbrunet@baylibre.com, martin.blumenstingl@googlemail.com, linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, rockosov@gmail.com Subject: Re: [PATCH v5 2/2] media: rc: introduce Meson IR TX driver Message-ID: <20210716082405.GA30719@gofer.mess.org> References: <20210714212706.24945-1-viktor.prutyanov@phystech.edu> <20210714212706.24945-3-viktor.prutyanov@phystech.edu> <20210715214001.GA25809@gofer.mess.org> <20210716013652.248bce6f@192.168.1.3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210716013652.248bce6f@192.168.1.3> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Viktor, On Fri, Jul 16, 2021 at 01:36:52AM +0300, Viktor Prutyanov wrote: > Hi Sean, > > On Thu, 15 Jul 2021 22:40:01 +0100 > Sean Young wrote: > > > On Thu, Jul 15, 2021 at 12:27:06AM +0300, Viktor Prutyanov wrote: > > + meson_irtx_fill_buf(ir, tx_buf, buf, len); > > > + dev_dbg(ir->dev, "TX buffer filled, length = %u\n", len); > > > + > > > + spin_lock_irqsave(&ir->lock, flags); > > > + meson_irtx_update_buf(ir, tx_buf, len, 0); > > > + reinit_completion(&ir->completion); > > > + meson_irtx_send_buffer(ir); > > > + spin_unlock_irqrestore(&ir->lock, flags); > > > + > > > + ret = wait_for_completion_interruptible(&ir->completion); > > > + dev_dbg(ir->dev, "TX %s\n", ret ? "interrupted" : > > > "completed"); > > > > Here two things can happen. One is, the process received a signal > > (e.g. ^C). The other is that the hardware didn't issue any interrupts > > due some problem somewhere. In the latter case, we only escape this > > wait_for_completion_interruptable() when the user gets fed up and > > presses ^C or something like that. > > > > > + > > > + spin_lock_irqsave(&ir->lock, flags); > > > + kfree(ir->buf); > > > + meson_irtx_update_buf(ir, NULL, 0, 0); > > > + spin_unlock_irqrestore(&ir->lock, flags); > > > > Now it is possible that the buffer gets cleared before that IR was > > sent, if the signal was received early enough. This means not all the > > Tx was completed. > > > > > + > > > + return len; > > > > Yet, we always return success. > > > > In case no interrupts were generated we should return an error in a > > timely manner, so the wait_for_completion() needs the timeout. You > > can use the fact that the IR is never longer IR_MAX_DURATION (half a > > second currently). Not sure what the returned error should be, maybe > > -ETIMEDOUT? > > As for me, ETIMEDOUT is OK. > > > > The problem with the interruptable wait is that a process can receive > > a signal at any time, and now when this happens your IR gets > > truncated. I don't think this is what you want. > > Should I replace wait_for_completion_interruptible by > wait_for_completion_timeout in order to wait in uninterruptible way? Yes, the process can receive a signal if the terminal is resized (SIGWINCH) or if the process is backgrounded and then foregrounded with ^Z and fg (SIGCONT). If this happens during tx then the tx might be incomplete. Thanks, Sean