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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 5C152C433E7 for ; Mon, 12 Oct 2020 17:04:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0BEC62072D for ; Mon, 12 Oct 2020 17:04:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=lechnology.com header.i=@lechnology.com header.b="k/NrFvl5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403883AbgJLRER (ORCPT ); Mon, 12 Oct 2020 13:04:17 -0400 Received: from vern.gendns.com ([98.142.107.122]:56706 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390355AbgJLRER (ORCPT ); Mon, 12 Oct 2020 13:04:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lechnology.com; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :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=zJY3Dr6AnVYzWq6bCyK4S4rlKOnb0m8nFs+n4rj0aqA=; b=k/NrFvl5XJsTY+RGXOx8Q7rgV5 6WNNASc5T2nH77d9p4WJ5StsyyoafuyjaX7OIUA/cx9AzZCWgCRdBuECQRkacLzZujA1K1NtbFU9c KT8ra/6X+hfinxyRa8siQlResVDcawWPR3ET4bVDjn+XY2LOmvomALeWmTn4JL19k/gC+3IkGygGh WGAyhJUf0R5CDBejIe3Sr7wUWTQl8qhMG11CkFDMgw3zPBV8NQ1L+CdhHkXbHHuBBNBLcUxWHtbMt Q02yv7CcfFESjhKZTjKfgLviYlVIbGFNkkQZefNDtOBRrc2s4OMTLDJxaB1PKao2OkQWTGL3nL+ME t4YRc7kQ==; Received: from [2600:1700:4830:165f::19e] (port=46758) by vern.gendns.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1kS1F6-00009H-9o; Mon, 12 Oct 2020 13:04:12 -0400 Subject: Re: [PATCH v5 4/5] docs: counter: Document character device interface To: William Breathitt Gray , Pavel Machek Cc: jic23@kernel.org, kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com, patrick.havelange@essensium.com, fabrice.gasnier@st.com, mcoquelin.stm32@gmail.com, alexandre.torgue@st.com References: <54190f9875b81b6aa5483a7710b084053a44abb8.1601170670.git.vilhelm.gray@gmail.com> <20201008080909.GA31561@amd> <20201008122845.GA3314@shinobu> From: David Lechner Message-ID: Date: Mon, 12 Oct 2020 12:04:10 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201008122845.GA3314@shinobu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On 10/8/20 7:28 AM, William Breathitt Gray wrote: > On Thu, Oct 08, 2020 at 10:09:09AM +0200, Pavel Machek wrote: >> Hi! >> >>> + int main(void) >>> + { >>> + struct pollfd pfd = { .events = POLLIN }; >>> + struct counter_event event_data[2]; >>> + >>> + pfd.fd = open("/dev/counter0", O_RDWR); >>> + >>> + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches); >>> + ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches + 1); >>> + ioctl(pfd.fd, COUNTER_LOAD_WATCHES_IOCTL); >>> + >>> + for (;;) { >>> + poll(&pfd, 1, -1); >> >> Why do poll, when you are doing blocking read? >> >>> + read(pfd.fd, event_data, sizeof(event_data)); >> >> Does your new chrdev always guarantee returning complete buffer? >> >> If so, should it behave like that? >> >> Best regards, >> Pavel >> -- >> (english) http://www.livejournal.com/~pavelmachek >> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html > > I suppose you're right: a poll() should be redundant now with this > version of the character device implementation because buffers will > always return complete; so a blocking read() should achieve the same > behavior that a poll() with read() would. > > I'll give some more time for additional feedback to come in for this > version of the patchset, and then likely remove support for poll() in > the v6 submission. > > William Breathitt Gray > I hope that you mean that you will just remove it from the example and not from the chardev. Otherwise it won't be possible to integrate this with an event loop.