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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 B24B1C04EBF for ; Mon, 23 Sep 2019 13:58:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D7D520882 for ; Mon, 23 Sep 2019 13:58:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408338AbfIWN6p (ORCPT ); Mon, 23 Sep 2019 09:58:45 -0400 Received: from mx1.emlix.com ([188.40.240.192]:42148 "EHLO mx1.emlix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2408320AbfIWN6o (ORCPT ); Mon, 23 Sep 2019 09:58:44 -0400 Received: from mailer.emlix.com (unknown [81.20.119.6]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.emlix.com (Postfix) with ESMTPS id 476D85FBA6; Mon, 23 Sep 2019 15:58:43 +0200 (CEST) From: Philipp Puschmann To: linux-kernel@vger.kernel.org Cc: u.kleine-koenig@pengutronix.de, gregkh@linuxfoundation.org, yibin.gong@nxp.com, fugang.duan@nxp.com, l.stach@pengutronix.de, jslaby@suse.com, shawnguo@kernel.org, s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com, linux-imx@nxp.com, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Philipp Puschmann Subject: [PATCH v3] serial: imx: adapt rx buffer and dma periods Date: Mon, 23 Sep 2019 15:58:42 +0200 Message-Id: <20190923135842.956-1-philipp.puschmann@emlix.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Using only 4 DMA periods for UART RX is very few if we have a high frequency of small transfers - like in our case using Bluetooth with many small packets via UART - causing many dma transfers but in each only filling a fraction of a single buffer. Such a case may lead to the situation that DMA RX transfer is triggered but no free buffer is available. When this happens dma channel ist stopped - with the patch "dmaengine: imx-sdma: fix dma freezes" temporarily only - with the possible consequences that: with disabled hw flow control: If enough data is incoming on UART port the RX FIFO runs over and characters will be lost. What then happens depends on upper layer. with enabled hw flow control: If enough data is incoming on UART port the RX FIFO reaches a level where CTS is deasserted and remote device sending the data stops. If it fails to stop timely the i.MX' RX FIFO may run over and data get lost. Otherwise it's internal TX buffer may getting filled to a point where it runs over and data is again lost. It depends on the remote device how this case is handled and if it is recoverable. Obviously we want to avoid having no free buffers available. So we decrease the size of the buffers and increase their number and the total buffer size. Signed-off-by: Philipp Puschmann Reviewed-by: Lucas Stach --- Changelog v4: - fix total buffer size Changelog v3: - enhance description Changelog v2: - split this patch from series "Fix UART DMA freezes for iMX6" - add Reviewed-by tag drivers/tty/serial/imx.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 87c58f9f6390..51dc19833eab 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -1034,8 +1034,6 @@ static void imx_uart_timeout(struct timer_list *t) } } -#define RX_BUF_SIZE (PAGE_SIZE) - /* * There are two kinds of RX DMA interrupts(such as in the MX6Q): * [1] the RX DMA buffer is full. @@ -1118,7 +1116,8 @@ static void imx_uart_dma_rx_callback(void *data) } /* RX DMA buffer periods */ -#define RX_DMA_PERIODS 4 +#define RX_DMA_PERIODS 16 +#define RX_BUF_SIZE (RX_DMA_PERIODS * PAGE_SIZE / 4) static int imx_uart_start_rx_dma(struct imx_port *sport) { -- 2.23.0