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 CF3BBC4332F for ; Tue, 18 Jan 2022 03:04:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345829AbiARDEL (ORCPT ); Mon, 17 Jan 2022 22:04:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345915AbiARCsz (ORCPT ); Mon, 17 Jan 2022 21:48:55 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 82F0BC06174E; Mon, 17 Jan 2022 18:39:39 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 24BBEB8125F; Tue, 18 Jan 2022 02:39:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF0CDC36AEB; Tue, 18 Jan 2022 02:39:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642473577; bh=s/Gb1+A0zdS6AV7USnmioZzAIOaTo9cubpQqrOa/pnA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=N90EAq8SrnIFnnVF/k6RjWu1IRleFZEk4/8SfSS+cidW0W5VGCPb4UeFM+tDj0JaN b6f4nQVA1616P8Y+tN7PawdRRa2+kn5rNcQYuZJyGUUO3tdnwmZQPKSduFRrWbIVgs DQFC9B7Ngzbw6xTpwXd1PYrAOK+FoHktAq1gMV3lyW8g6PlCr6Wv8iTZMx004lFyhG 10xSFX3l8uNnwgh8cNYRmTNPVQorywTzHGRtR0Pcl8QPT3TIvcvwpcufd+OCWnQVrT 6dUdyPv4SfzuP5wxu7d5P/vKoWRYSzQw94gR422c1rV0qUt3/vv60LeNMdYmaaZx8y giefyDf8GXo/g== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Lukas Wunner , Russell King , Greg Kroah-Hartman , Sasha Levin , linux@armlinux.org.uk, jirislaby@kernel.org, linux-serial@vger.kernel.org Subject: [PATCH AUTOSEL 5.15 177/188] serial: pl011: Drop CR register reset on set_termios Date: Mon, 17 Jan 2022 21:31:41 -0500 Message-Id: <20220118023152.1948105-177-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220118023152.1948105-1-sashal@kernel.org> References: <20220118023152.1948105-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lukas Wunner [ Upstream commit e368cc656fd6d0075f1c3ab9676e2001451e3e04 ] pl011_set_termios() briefly resets the CR register to zero, thereby glitching DTR/RTS signals. With rs485 this may result in the bus being occupied for no reason. Where does this register write originate from? The PL011 driver was forked from the PL010 driver in 2004: https://git.kernel.org/history/history/c/157c0342e591 Until this commit, the PL010 driver's IRQ handler ambauart_int() modified the CR register without holding the port spinlock. ambauart_set_termios() also modified that register. To prevent concurrent read-modify-writes by the IRQ handler and to prevent transmission while changing baudrate, ambauart_set_termios() had to disable interrupts. On the PL010, that is achieved by writing zero to the CR register. However, on the PL011, interrupts are disabled in the IMSC register, not in the CR register. Additionally, the commit amended both the PL010 and PL011 driver to acquire the port spinlock in the IRQ handler, obviating the need to disable interrupts in ->set_termios(). So the CR register write is obsolete for two reasons. Drop it. Cc: Russell King Signed-off-by: Lukas Wunner Link: https://lore.kernel.org/r/f49f945375f5ccb979893c49f1129f51651ac738.1641129062.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/amba-pl011.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 52518a606c06a..9b1b0d9bdf7be 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -2105,9 +2105,7 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios, if (port->rs485.flags & SER_RS485_ENABLED) termios->c_cflag &= ~CRTSCTS; - /* first, disable everything */ old_cr = pl011_read(uap, REG_CR); - pl011_write(0, uap, REG_CR); if (termios->c_cflag & CRTSCTS) { if (old_cr & UART011_CR_RTS) -- 2.34.1