From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 09CC3606A32D for ; Tue, 3 Nov 2026 18:07:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=EDdENs6O Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4jJxNk5Pkjz2xjM; Wed, 04 Nov 2026 05:07:02 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=192.198.163.14 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1793729222; cv=none; b=j+LCZuY2AkpnBFCoq8zaZ4gU7lHS2BSG8Tr67X4SpQ2o6LtABk3V3OuGcVrq1NhcA/0ZAUctcxlu4wNyOgjDNPXfOYUI+V+80HK25ZHQr2yPqZWZSIk15COA/PvhU/SSShcmMuaBFKc/8LOWoFu1NE0fC7d0S8IVja6GA1QpgSmntbMFQMl+cO7zo70iBxCCpeqCv5R0zM8b/WoQS82CpdfM2C/zGkc/6GSPXzL+8cvb7QVg6tuzssD5EXUZ/BwCfzLQZP5fgUWiROj3lQVKePWNrFbKqbag/sOqOaQG7so1qS9RQ0GBo875L2PRXC7n959ENxgi9ue0uEcjj/NznA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1793729222; c=relaxed/relaxed; bh=w5lVWBJjRjA2krxM/KTY4SL80JsSZ9imdxqcG/GS5Zk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ArwQ+drA8TXf5C/bislCICZBcMTyOl1dyICi90iBK7Q9a6/3xcYfkfuX/Zipx9av/9f26SsrnbNPnD7ZHc3Wgk5tGSmIEoFytPDeQX/7ZTtxkL2MqZu/vkqDhorcSTrgetGQ9khs21UNoVRXQToSR/+lCa8/ilZ7vjh9ZOP3dhOS6WVFb6PqalRxtVtWmnIP26FpVsz3jDXOsYsKeSiSw+34RQbjMQFpOylKbFzfATO7ttPNF4xFpBYIweATKnkUGnLbxGmRfYDtiaGIa3Nu3pqeZiAxg1NRErJWwaxTCP3IY+X1hIHJgfa2TU3P9t75Y/FdDb9vDmf/CxUGl5KdQQ== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=EDdENs6O; dkim-atps=neutral; spf=pass (client-ip=192.198.163.14; helo=mgamail.intel.com; envelope-from=andriy.shevchenko@linux.intel.com; receiver=lists.ozlabs.org) smtp.mailfrom=linux.intel.com Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=EDdENs6O; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.intel.com (client-ip=192.198.163.14; helo=mgamail.intel.com; envelope-from=andriy.shevchenko@linux.intel.com; receiver=lists.ozlabs.org) Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4jJxNh28fLz2xdX for ; Wed, 04 Nov 2026 05:06:58 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1793729221; x=1825265221; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=bfpjoi+2x7WliPDN0Q0PNRLL9EnvniyukWyol0qacZo=; b=EDdENs6OVuJr1T2cCF0cPHO1+tt9VgjwNDcFshWljssRye2qrjdsVZPo IKavNxOjFIAU1cOsLvrnCWM8hX/POUGHuiK9sW7HwneZu+ELMD1TDneOz NYizWMPbi9p2mu4LMXdhPE/wCmz0h6VFTe0vCCUi/wMxmJDn+JlzNcdlS sk4M8A+DDS8bELPDolQ/KYo3NzIjv9V1XwUSqwwvTcMN5KvAM6T00JRLu ghrWRQwEN2cQqbrSLLD6tEkqa7yu//KJHzv7jWNZZrxmaiYvM+MJevQDh WOqMKvCxhn5B4IL80jKaJoBpZNXyA/cE/8aa07Ap1c8qZrMgJCdGd6I9D A==; X-CSE-ConnectionGUID: 7KGiX6duRHy39eeootzgmQ== X-CSE-MsgGUID: BWT3rmM1T0mR1zgawrDo7A== X-IronPort-AV: E=McAfee;i="6800,10657,11955"; a="2497319" X-IronPort-AV: E=Sophos;i="6.27,193,1787036400"; d="scan'208";a="2497319" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Nov 2026 10:06:57 -0800 X-CSE-ConnectionGUID: 0DUEqvTGSyWP84YdvsRCVw== X-CSE-MsgGUID: pmuQBEc9QCOEV5T43CA1cw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,193,1787036400"; d="scan'208";a="6503533" Received: from ettammin-mobl3.ger.corp.intel.com (HELO localhost) ([10.245.245.108]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Nov 2026 10:06:50 -0800 Date: Tue, 3 Nov 2026 20:06:47 +0200 From: Andy Shevchenko To: James Hilliard Cc: Greg Kroah-Hartman , Jiri Slaby , Raul E Rangel , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Heikki Krogerus , Tony Lindgren , Sebastian Andrzej Siewior , Richard Genoud , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , Jacky Huang , Shan-Chun Hung , Pali =?iso-8859-1?Q?Roh=E1r?= , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , "Maciej W. Rozycki" , Timur Tabi , Peter Ujfalusi , Vignesh Raghavendra , Patrice Chotard , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v9 7/8] serial: 8250: retire canceled RX DMA before reusing the receive buffer Message-ID: References: <20261102-submit-serial-8250-dma-cancel-v1-v9-0-9159caade148@gmail.com> <20261102-submit-serial-8250-dma-cancel-v1-v9-7-9159caade148@gmail.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs, Bertel Jungin Aukio 5, 02600 Espoo X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 10:54:38AM -0700, James Hilliard wrote: > On Tue, Nov 3, 2026 at 10:34 AM Andy Shevchenko > wrote: > > On Mon, Nov 02, 2026 at 04:14:34PM -0700, James Hilliard wrote: ... > > > +static void serial8250_rx_dma_flush_work(struct work_struct *work) > > > +{ > > > + struct uart_8250_dma *dma = container_of(work, struct uart_8250_dma, rx_flush_work); > > > + struct uart_8250_port *p = dma->port; > > > + unsigned int delay_us = USEC_PER_MSEC; > > > + ktime_t start = ktime_get(); > > > + bool recover, retry, restore_rx; > > > + bool warned = false; > > > + int ret; > > > + > > > + guard(serial8250_rpm)(p); > > > + > > > + for (;;) { > > > + scoped_guard(uart_port_lock_irqsave, &p->port) { > > > + /* Shutdown cancels this work and drains both DMA channels. */ > > > + if (dma->shutting_down) > > > + return; > > > + /* Serialize reset with completion and shutdown notifications. */ > > > + WRITE_ONCE(dma->rx_pause_wakeup, false); > > > + retry = dma->rx_pause_pending && !dma->rx_terminating; > > > + if (retry) { > > > + ret = serial8250_rx_dma_try_flush(p); > > > + retry = dma->rx_pause_pending && !dma->rx_terminating; > > > + } > > > + recover = dma->rx_err; > > > + } > > > + if (!retry) > > > + break; > > > + if (!warned && ktime_ms_delta(ktime_get(), start) >= MSEC_PER_SEC) { > > > + dev_warn_ratelimited(p->port.dev, > > > + "RX DMA pause stalled: %d; retaining transfer and retrying\n", > > > + ret); > > > > _ratelimited() is a slop of AI without understanding the code. It makes nonsense > > in combination with warned. > > The two controls have different scopes. warned is local to one invocation > of the flush worker and prevents repeated warning attempts while that > flush remains stalled. A later flush starts with warned cleared again. > > The rate limit applies across worker invocations and UART ports. It limits > messages from separate stalls, rather than repeated retries of the same > stall. How? The whole _ratelimited() is nonsense here. > > > + warned = true; > > > > Altogether NIH _once(). > > dev_warn_once() uses a static flag at the call site, shared by all ports. > After the first warning, subsequent stalls would remain silent even after > recovery or reopening the port, including stalls on another UART. > > The intended behavior here is at most one warning attempt per prolonged > stall, while keeping later incidents diagnosable and limiting their > aggregate logging rate. Yes, so what the point to use _ratelimited()? > > > + } > > > + /* Notifications also cover completion or shutdown before sleeping. */ > > > + wait_event_hrtimeout(dma->rx_pause_wait, READ_ONCE(dma->rx_pause_wakeup), > > > + ns_to_ktime(delay_us * NSEC_PER_USEC)); > > > + delay_us = min(delay_us * 2, USEC_PER_SEC); > > > + } > > > + > > > + if (recover) { > > > + ret = dmaengine_terminate_sync(dma->rxchan); > > > + if (ret) { > > > + /* Retain ownership and keep RX masked if DMA cannot be stopped. */ > > > + dev_err(p->port.dev, "failed to stop RX DMA: %d\n", ret); > > > + return; > > > + } > > > + } else { > > > + dmaengine_synchronize(dma->rxchan); > > > + } > > > + > > > + scoped_guard(uart_port_lock_irqsave, &p->port) { > > > + restore_rx = recover || dma->rx_pause_pending; > > > + dma->rx_pause_pending = false; > > > + dma->rx_terminating = false; > > > + dma->rx_running = 0; > > > + if (dma->shutting_down) > > > + return; > > > + > > > + if (!restore_rx) > > > + return; > > > + > > > + /* Apply the current enables, including any intervening stop_rx(). */ > > > + serial8250_out_IER(p, p->ier); > > > + } > > > + if (recover) > > > + dev_warn(p->port.dev, "RX DMA failed, using PIO\n"); > > > } -- With Best Regards, Andy Shevchenko