From patchwork Thu Oct 1 07:44:15 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Thomas Petazzoni X-Patchwork-Id: 267074 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=-12.7 required=3.0 tests=BAYES_00, 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 79F98C4727C for ; Thu, 1 Oct 2020 07:44:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 417DA2158C for ; Thu, 1 Oct 2020 07:44:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725883AbgJAHoX (ORCPT ); Thu, 1 Oct 2020 03:44:23 -0400 Received: from relay9-d.mail.gandi.net ([217.70.183.199]:50805 "EHLO relay9-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725878AbgJAHoV (ORCPT ); Thu, 1 Oct 2020 03:44:21 -0400 X-Originating-IP: 86.206.245.199 Received: from localhost (lfbn-tou-1-420-199.w86-206.abo.wanadoo.fr [86.206.245.199]) (Authenticated sender: thomas.petazzoni@bootlin.com) by relay9-d.mail.gandi.net (Postfix) with ESMTPSA id 0D7FDFF80B; Thu, 1 Oct 2020 07:44:17 +0000 (UTC) From: Thomas Petazzoni To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, =?utf-8?q?Jan_Kundr=C3=A1t?= , Mark Brown , Andy Shevchenko , linux-spi@vger.kernel.org, Thomas Petazzoni Subject: [PATCH v2] serial: max310x: rework RX interrupt handling Date: Thu, 1 Oct 2020 09:44:15 +0200 Message-Id: <20201001074415.349739-1-thomas.petazzoni@bootlin.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 X-GND-Spam-Score: 400 X-GND-Status: SPAM Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Currently, the RX interrupt logic uses the RXEMPTY interrupt, with the RXEMPTYINV bit set, which means we get an RX interrupt as soon as the RX FIFO is non-empty. However, with the MAX310X having a FIFO of 128 bytes, this makes very poor use of the FIFO: we trigger an interrupt as soon as the RX FIFO has one byte, which means a lot of interrupts, each only collecting a few bytes from the FIFO, causing a significant CPU load. Instead this commit relies on two other RX interrupt events: - MAX310X_IRQ_RXFIFO_BIT, which triggers when the RX FIFO has reached a certain threshold, which we define to be half of the FIFO size. This ensure we get an interrupt before the RX FIFO fills up. - MAX310X_LSR_RXTO_BIT, which triggers when the RX FIFO has received some bytes, and then no more bytes are received for a certain time. Arbitrarily, this time is defined to the time is takes to receive 4 characters. On a Microchip SAMA5D3 platform that is receiving 20 bytes every 16ms over one MAX310X UART, this patch has allowed to reduce the CPU consumption of the interrupt handler thread from ~25% to 6-7%. Signed-off-by: Thomas Petazzoni Tested-by: Jan Kundrát Reviewed-by: Jan Kundrát --- Changes since v1: - Fix missing space when closing a comment --- drivers/tty/serial/max310x.c | 29 ++++++++++++++++++++++++----- 1 file changed, 24 insertions(+), 5 deletions(-) diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c index 8434bd5a8ec7..21130af106bb 100644 --- a/drivers/tty/serial/max310x.c +++ b/drivers/tty/serial/max310x.c @@ -1056,9 +1056,9 @@ static int max310x_startup(struct uart_port *port) max310x_port_update(port, MAX310X_MODE1_REG, MAX310X_MODE1_TRNSCVCTRL_BIT, 0); - /* Configure MODE2 register & Reset FIFOs*/ - val = MAX310X_MODE2_RXEMPTINV_BIT | MAX310X_MODE2_FIFORST_BIT; - max310x_port_write(port, MAX310X_MODE2_REG, val); + /* Reset FIFOs */ + max310x_port_write(port, MAX310X_MODE2_REG, + MAX310X_MODE2_FIFORST_BIT); max310x_port_update(port, MAX310X_MODE2_REG, MAX310X_MODE2_FIFORST_BIT, 0); @@ -1086,8 +1086,27 @@ static int max310x_startup(struct uart_port *port) /* Clear IRQ status register */ max310x_port_read(port, MAX310X_IRQSTS_REG); - /* Enable RX, TX, CTS change interrupts */ - val = MAX310X_IRQ_RXEMPTY_BIT | MAX310X_IRQ_TXEMPTY_BIT; + /* + * Let's ask for an interrupt after a timeout equivalent to + * the receiving time of 4 characters after the last character + * has been received. + */ + max310x_port_write(port, MAX310X_RXTO_REG, 4); + + /* + * Make sure we also get RX interrupts when the RX FIFO is + * filling up quickly, so get an interrupt when half of the RX + * FIFO has been filled in. + */ + max310x_port_write(port, MAX310X_FIFOTRIGLVL_REG, + MAX310X_FIFOTRIGLVL_RX(MAX310X_FIFO_SIZE / 2)); + + /* Enable RX timeout interrupt in LSR */ + max310x_port_write(port, MAX310X_LSR_IRQEN_REG, + MAX310X_LSR_RXTO_BIT); + + /* Enable LSR, RX FIFO trigger, CTS change interrupts */ + val = MAX310X_IRQ_LSR_BIT | MAX310X_IRQ_RXFIFO_BIT | MAX310X_IRQ_TXEMPTY_BIT; max310x_port_write(port, MAX310X_IRQEN_REG, val | MAX310X_IRQ_CTS_BIT); return 0;