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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6AD8C433EF for ; Tue, 4 Jan 2022 10:43:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230183AbiADKnh (ORCPT ); Tue, 4 Jan 2022 05:43:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229644AbiADKnh (ORCPT ); Tue, 4 Jan 2022 05:43:37 -0500 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F822C061761 for ; Tue, 4 Jan 2022 02:43:37 -0800 (PST) Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[IPv6:::1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1n4hHm-0007Mm-Mq; Tue, 04 Jan 2022 11:43:22 +0100 Subject: Re: [PATCH] serial: imx: reduce RX interrupt frequency To: =?UTF-8?Q?Tomasz_Mo=c5=84?= , linux-serial@vger.kernel.org Cc: Jiri Slaby , Greg Kroah-Hartman , Sascha Hauer , NXP Linux Team , Pengutronix Kernel Team , Shawn Guo , Fabio Estevam , k.drobinski@camlintechnologies.com References: <20220104103203.2033673-1-tomasz.mon@camlingroup.com> From: Ahmad Fatoum Message-ID: Date: Tue, 4 Jan 2022 11:43:21 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20220104103203.2033673-1-tomasz.mon@camlingroup.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: a.fatoum@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-serial@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On 04.01.22 11:32, Tomasz Moń wrote: > Triggering RX interrupt for every byte defeats the purpose of aging > timer and leads to interrupt starvation at high baud rates. s/starvation/storm/ ? > > Increase receiver trigger level to 8 to increase the minimum period > between RX interrupts to 8 characters time. The tradeoff is increased > latency. In the worst case scenario, where RX data has intercharacter > delay slightly less than aging timer (8 characters time), it can take > up to 63 characters time for the interrupt to be raised since the > reception of the first character. > > Signed-off-by: Tomasz Moń > --- > drivers/tty/serial/imx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c > index 90f82e6c54e4..3c812c47ecc0 100644 > --- a/drivers/tty/serial/imx.c > +++ b/drivers/tty/serial/imx.c > @@ -1255,7 +1255,7 @@ static void imx_uart_clear_rx_errors(struct imx_port *sport) > } > > #define TXTL_DEFAULT 2 /* reset default */ > -#define RXTL_DEFAULT 1 /* reset default */ > +#define RXTL_DEFAULT 8 /* 8 characters or aging timer */ > #define TXTL_DMA 8 /* DMA burst setting */ > #define RXTL_DMA 9 /* DMA burst setting */ > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |