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 EDCF5C433F5 for ; Tue, 18 Jan 2022 03:18:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351056AbiARDR5 (ORCPT ); Mon, 17 Jan 2022 22:17:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353246AbiARDIs (ORCPT ); Mon, 17 Jan 2022 22:08:48 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C182CC061759; Mon, 17 Jan 2022 18:51:11 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 309EC61348; Tue, 18 Jan 2022 02:51:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BBB7C36AEF; Tue, 18 Jan 2022 02:51:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642474270; bh=zgJycrBY7VvfgIA9nrpGkp89cc0lhlwKiFUFwBPoQBU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EkfI83w7vaFIITe85s7QqbHmW5IPWUTOYPmyaWNWf6QytBpEQfjWD7TNVMueOew85 s80zdMn4j1ZRFwrxB31utUUVLfFTTNVDZ/U55VP4HSNQpJfLh6RixawM1fNGwQnDyx vmIDtekgK8lHS+AZJSrdJp147W7n/5Q3z4gD5JdKLua4md9/zn/igxtQqvi9nRjqnh GGgRNAIRSNGybM7vr2g6Ia+EgmfLNr56qcQXR+LVcv5Rbnjq9bHN5K//ioAU9M92hD EWLGRFkzull6+QekDjGKGwa8lMA5NLw0G/1+wnpaFRnI8Q7HIY7WExaXzDWcqYi3Z0 zgh385EUfnxCg== 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 4.14 54/56] serial: pl010: Drop CR register reset on set_termios Date: Mon, 17 Jan 2022 21:49:06 -0500 Message-Id: <20220118024908.1953673-54-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220118024908.1953673-1-sashal@kernel.org> References: <20220118024908.1953673-1-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-serial@vger.kernel.org From: Lukas Wunner [ Upstream commit 08a0c6dff91c965e39905cf200d22db989203ccb ] pl010_set_termios() briefly resets the CR register to zero. Where does this register write come from? The PL010 driver's IRQ handler ambauart_int() originally 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. That is achieved by writing zero to the CR register. However in 2004 the PL010 driver was amended to acquire the port spinlock in the IRQ handler, obviating the need to disable interrupts in ->set_termios(): https://git.kernel.org/history/history/c/157c0342e591 That rendered the CR register write obsolete. Drop it. Cc: Russell King Signed-off-by: Lukas Wunner Link: https://lore.kernel.org/r/fcaff16e5b1abb4cc3da5a2879ac13f278b99ed0.1641128728.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/amba-pl010.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/drivers/tty/serial/amba-pl010.c b/drivers/tty/serial/amba-pl010.c index 9ec4b8d2879f7..0698fbf3b6d61 100644 --- a/drivers/tty/serial/amba-pl010.c +++ b/drivers/tty/serial/amba-pl010.c @@ -465,14 +465,11 @@ pl010_set_termios(struct uart_port *port, struct ktermios *termios, if ((termios->c_cflag & CREAD) == 0) uap->port.ignore_status_mask |= UART_DUMMY_RSR_RX; - /* first, disable everything */ old_cr = readb(uap->port.membase + UART010_CR) & ~UART010_CR_MSIE; if (UART_ENABLE_MS(port, termios->c_cflag)) old_cr |= UART010_CR_MSIE; - writel(0, uap->port.membase + UART010_CR); - /* Set baud rate */ quot -= 1; writel((quot & 0xf00) >> 8, uap->port.membase + UART010_LCRM); -- 2.34.1