Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Sherry Sun <sherry.sun@nxp.com>
To:     gregkh@linuxfoundation.org, jirislaby@kernel.org
Cc:     linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-imx@nxp.com
Subject: [PATCH] tty: serial: fsl_lpuart: make sure to turn off break before enabling CTS
Date:   Tue, 16 May 2023 18:11:38 +0800
Message-Id: <20230516101138.24179-1-sherry.sun@nxp.com>
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?4hW/GL4MAoqfFhSASW5YaKoylVN5cDFuBUMc699ExgLDZiU36vw/DG6qoPii?=
 =?us-ascii?Q?brfmti4zRdXnJ46hipyVRjvNay/xWZNmn5y90h1QlBUCVxa1CwnqkkJEx2U4?=
 =?us-ascii?Q?MCYmDjCmuAUh4OnFc1wuKxbmzkQNXvHNK09nIif+kK1WKiKsazI9c50wR7fF?=
 =?us-ascii?Q?waC0PCuHf1SxHuV9SCz+7gSMC4V5FGYK87Bil1W0ULN7uIJPi/ffI9n5syLr?=
 =?us-ascii?Q?5WC9dp3BjphRAZDVZmRLq2zR8x0wM/ICEw2pLHcl7lkG82614KaoQD0sKRGq?=
 =?us-ascii?Q?r9MfXDBWC5kxiWEA3FWEB0G9bX0TcMwSrWWIMQTCSGwrSKG4Lhlyx6V4xoI5?=
 =?us-ascii?Q?zw4dG5ury+DUPjFk1QbCToosPRbVa/dAJy+7SIxTM9FSbCThxrOxrWETSU6D?=
 =?us-ascii?Q?NjWm1TYPHdV3Ai0/TjEF2L5QVyIkvM75o6a3dighnZgqQpD8kvYws92GuRPn?=
 =?us-ascii?Q?dR7z1FnYxUfrXgg868zjI9bzvRU/rFhD0JkuMFOf1Hev3VcjBrPV8fFWf9f0?=
 =?us-ascii?Q?QB/7wTEP153fRzr0ANoFGJdDjUgUttJLd+d+0Yf+A4+Ue4XojPNp7LSnMswY?=
 =?us-ascii?Q?is+h76bHKhbudJ7j/LwqfvR1LvHcXl5DenxnmMaNiFnFwpK0tFYLrItwwyAn?=
 =?us-ascii?Q?DkU5ST3fnTd1bQbSZKEFjJiSyr3lEYmCQg+Uu1gfeujmKYvrJB30N2cXiYFE?=
 =?us-ascii?Q?6TV1/qi23bvHYCAjQL7OipbOdG1+zTzZVqXaOVD5MQ9uDqr35P+hrPw/rjbo?=
 =?us-ascii?Q?BmtK0b3APo4+pJtwe9rHp8Si8/m2DURfF1Vw/XgVzBy80rAtP3M7QZtnHxoC?=
 =?us-ascii?Q?1eMPIFk4u9bI5mvho981dDXfgPubr4pfe/iOKNyhDH2+JUTBBD56jOi7+Di4?=
 =?us-ascii?Q?ArO9N1FVCqoQjfJaz2Fhw9p6IeG/nM2yxnpqzWtCxco1jWfRtFjF/UZFntp+?=
 =?us-ascii?Q?dCCPe0k94rhsiCm/nrlO3AZ1FZfq9RQY5/A4rSWveVu7gMZ5ufXSAhC+9Xb1?=
 =?us-ascii?Q?Nk5uK3vOtbquvzLF99IhMjfBTke1exsT+z1O434FWeJCVCYNmkXEO5ttlNDk?=
 =?us-ascii?Q?uYBDl2Ux7Hig1eXWQW2Wx4VVl7LGwf+QfSMVGzlfE3YwTjfU5gUQFXZ+O2kn?=
 =?us-ascii?Q?blxxUUYSIsvQMu6oUTsOepghWD1gD0uyMC/7prmljpfy+2ZFnR6ON3hvkRe8?=
 =?us-ascii?Q?YRmWvIb1dOpf462pbwimcbUG12pGT4Ys+5vt26aJmfoW2Nz+56u0QDnXQPTs?=
 =?us-ascii?Q?FZnCDq4khB98fCERRJsWchY4OIgOp0UnCRK57R3wb6JfqiLTwB5PK/KtZXfh?=
 =?us-ascii?Q?bDbWQobiSt6dAqsIicYhAJs9C0gxhKmxzwGVBAII3vrcLShKSRFFZXrgFrZJ?=
 =?us-ascii?Q?vFOurDriF5XPW7kVNsfSveoso2Q7h6mrxT3PL54WHpCvDBhgBmRHxHarq0am?=
 =?us-ascii?Q?NsZ99xmNyZdvTzTmTqa5+9Rs7MG3FQSmvlLOrX4FyeQnaoPQgLyPPe9SDD8D?=
 =?us-ascii?Q?9zR5DqIDOy/t1oK4nDW29aAZssPUa67oZGfMSrE4FSXePb1zsB4PqHYMhp7j?=
 =?us-ascii?Q?b/NFlh+mx/ULFC+tOyjH3d/NA96emSArTvvwhjaV?=
X-OriginatorOrg: nxp.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 2503af29-fd7d-4868-72e3-08db55f68e98
X-MS-Exchange-CrossTenant-AuthSource: AS8PR04MB8404.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 May 2023 10:16:04.7797
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: X82Q2wV0xpYSmRrZFPC0Ecx01JVZO+D8XBIva37i5zk3vUMhWi/musU8oCwc7IuCkqHbhHkD7J7yo0jQyH5rAg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR04MB8107
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS,T_SCC_BODY_TEXT_LINE,
        URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Due to one LPUART IP bug which treat the CTS as higher priority than the
break signal, that cause the break signal sending through UARTCTRL_SBK
may impacted by the CTS input if the HW flow control is enabled.

So commit c4c81db5cf8b ("tty: serial: fsl_lpuart: disable the CTS when
send break signal") try to workaround this IP issue, it disables CTS
before asserting SBK to avoid any interference from CTS, and re-enable
it when break off.

Here we enable CTS before turning off the break, there is still a risk
of the break signal been impacted by CTS input. The correct sequence is
to disable CTS before asserting SBK, and re-enable CTS after break off,
which ensures the break signal won't be impacted by CTS, so fix it.

Fixes: c4c81db5cf8b ("tty: serial: fsl_lpuart: disable the CTS when send break signal")
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
---
 drivers/tty/serial/fsl_lpuart.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 0e56fa64b4ce..d9e46f7b80e5 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1550,20 +1550,19 @@ static void lpuart32_break_ctl(struct uart_port *port, int break_state)
 	modem = lpuart32_read(port, UARTMODIR);
 
 	if (break_state != 0) {
-		temp |= UARTCTRL_SBK;
 		/*
 		 * LPUART CTS has higher priority than SBK, need to disable CTS before
 		 * asserting SBK to avoid any interference if flow control is enabled.
 		 */
 		if (cflag & CRTSCTS && modem & UARTMODIR_TXCTSE)
 			lpuart32_write(port, modem & ~UARTMODIR_TXCTSE, UARTMODIR);
+		lpuart32_write(port, temp | UARTCTRL_SBK, UARTCTRL);
 	} else {
-		/* Re-enable the CTS when break off. */
+		lpuart32_write(port, temp, UARTCTRL);
+		/* Re-enable the CTS after break off. */
 		if (cflag & CRTSCTS && !(modem & UARTMODIR_TXCTSE))
 			lpuart32_write(port, modem | UARTMODIR_TXCTSE, UARTMODIR);
 	}
-
-	lpuart32_write(port, temp, UARTCTRL);
 }
 
 static void lpuart_setup_watermark(struct lpuart_port *sport)
-- 
2.17.1