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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 C5F95C433E6 for ; Thu, 7 Jan 2021 18:17:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 825F92342C for ; Thu, 7 Jan 2021 18:17:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729252AbhAGSQz (ORCPT ); Thu, 7 Jan 2021 13:16:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35458 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729234AbhAGSQx (ORCPT ); Thu, 7 Jan 2021 13:16:53 -0500 Received: from mail-ej1-x62d.google.com (mail-ej1-x62d.google.com [IPv6:2a00:1450:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9243DC0612F5; Thu, 7 Jan 2021 10:16:08 -0800 (PST) Received: by mail-ej1-x62d.google.com with SMTP id g20so11076437ejb.1; Thu, 07 Jan 2021 10:16:08 -0800 (PST) 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=Xw3+iv4jWbYW97YeUypwG7nXusRKeVRrFbIKS0p0C4Q=; b=J6lRL3JoxLzgWSk2bres0wN6NMur16znBTo5G/6SfORLVzqj4LISPZgYwxFf1b93J0 5wU+iGKtasRmjtko9hRKqeQAjX5OcSSu2lgRmplNGM8r1qHQRAyN3WHf2D8LcEuAde5w /Yr7BzY69ZanYET+IXg0x2hQ16nqb8sbCDpUhMQIml4ikAQ7JmqX+z/v8S8+E3Q/E7MB +eDaijn9TOILv+OeM3q0Xo22swHJswkEWsL2M2dOmw2LR9ir8b+m/jDs9DDmTEOJBjTG Q8n9qwVsQEl+ou8Jn/GZUHpfxv1l9Z4+fyO5LSUyAMbTTweUXWvjuH0A+dOb7Re1RgcB /WIg== 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=Xw3+iv4jWbYW97YeUypwG7nXusRKeVRrFbIKS0p0C4Q=; b=FdqEC62XwZSuCb87gVFK3nO5E/7O1qNfCcXN80yzhhNJXhah2rglK6nUcfBmKfGarv l/4nqrCiPxrQtLTptmH+xSuJGhXzsZCcARdsbBjPTz4KUy8z2XvRArKgV3dxLPA+Fq2V EB62EYQqAM73mY1TxFlEizJTcnjJm7rwbfyu3ICVffye1ajAz3OECP5vfnkjohtcbfrH ybEODaTDYAF4T+2UdAcWVYopkDZnjtq7KxA9dRS2vDtmB0R4aECoPPM12KN1IjXko3NE H5T2Dm6IiGL3kos80ZVMpyEkmXhHk5PWO5c2gX/rmDyTYDoPbHDvu8vWmdu4IQTHQh4m u4Mg== X-Gm-Message-State: AOAM532XShD6zzeIITefQ+Re/td2XocC/PNMBhcIt53+pZT/BHN4/T69 QANL/GsdtYUtSg5rePAyI1g= X-Google-Smtp-Source: ABdhPJwK9ItKYY98MYFMnpwlqVeRDt7Zu9FaY6RcOPw0FA8Rl8SNjtzI2LmVs9WPpi6Ps4eSkyCo4Q== X-Received: by 2002:a17:906:3999:: with SMTP id h25mr47734eje.146.1610043367343; Thu, 07 Jan 2021 10:16:07 -0800 (PST) Received: from BV030612LT ([188.24.159.61]) by smtp.gmail.com with ESMTPSA id z12sm2739571ejr.17.2021.01.07.10.16.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Jan 2021 10:16:06 -0800 (PST) Date: Thu, 7 Jan 2021 20:16:04 +0200 From: Cristian Ciocaltea To: Greg Kroah-Hartman Cc: Jiri Slaby , Andreas =?iso-8859-1?Q?F=E4rber?= , Manivannan Sadhasivam , linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-actions@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger Message-ID: <20210107181604.GA427955@BV030612LT> References: <036c09732183a30eaab230884114f65ca42ca3b9.1609865007.git.cristian.ciocaltea@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, Thank you for the review! On Thu, Jan 07, 2021 at 04:20:55PM +0100, Greg Kroah-Hartman wrote: > On Tue, Jan 05, 2021 at 07:02:02PM +0200, Cristian Ciocaltea wrote: > > Implement 'poll_put_char' and 'poll_get_char' callbacks in struct > > 'owl_uart_ops' that enables OWL UART to be used for kernel debugging > > over serial line. > > > > Signed-off-by: Cristian Ciocaltea [...] > > + > > +static void owl_uart_poll_put_char(struct uart_port *port, unsigned char ch) > > +{ > > + while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU) > > + cpu_relax(); > > Unbounded loops? What could possibly go wrong? > > :( > > Please don't do that in the kernel, put a max bound on this. I didn't realize the issue since I had encountered this pattern in many other serial drivers, as well: altera_uart, arc_uart, atmel_serial, etc. > And are you _SURE_ that cpu_relax() is what you want to call here? I'm thinking of replacing the loop with 'readl_poll_timeout_atomic()', if that would be a better approach. Kind regards, Cristi > thanks, > > greg k-h