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 DACE4C4332F for ; Tue, 18 Jan 2022 02:33:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343819AbiARCdW (ORCPT ); Mon, 17 Jan 2022 21:33:22 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:43206 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345209AbiARCbW (ORCPT ); Mon, 17 Jan 2022 21:31:22 -0500 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 D2580B81239; Tue, 18 Jan 2022 02:31:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99FBFC36AE3; Tue, 18 Jan 2022 02:31:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642473079; bh=s/Gb1+A0zdS6AV7USnmioZzAIOaTo9cubpQqrOa/pnA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uEfhy/OlurBrx+x/5cRMbKoY3UEY/GqffY/HRXH9V3/yVqUWZQbVh+pUkxeWAnTAD puz/n6S7Ial6dn65sjjciwSVFcLfQFSFPF0cYO3hV4PFHWy/JaL/NiSVVM1ET8azx2 dbjrCqKfhTtiCQTcoEH0g8ErgNn741f9nLtBf/unGcnczRg1cJ9pFGJNxWLkGjrUac mXNUZARvLWMF9ZGQ8UIM+k4yE6FSE2v39Mad1LyGKcYEpzXPfZ+vm0Z+kuSEz8xUN4 MixvYFMGCc/2M+ZIrtLp1fVnLPSTecU36PC8TaaJhxNagxE+OQa7UroD0b4MEZPK4y AJECjJ5V9gnTQ== 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 5.16 206/217] serial: pl011: Drop CR register reset on set_termios Date: Mon, 17 Jan 2022 21:19:29 -0500 Message-Id: <20220118021940.1942199-206-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220118021940.1942199-1-sashal@kernel.org> References: <20220118021940.1942199-1-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: stable@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