tty/serial/imx: Enable TXEN bit in imx_poll_init().

mainline inclusion
from mainline-v5.121-rc1
commit aef1b6a2
category: bugfix
bugzilla: 108552 https://gitee.com/openeuler/kernel/issues/I4DDEL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aef1b6a27970607721a618a0b990716ca8dbbf9

-------------------------------------------------

As described in Documentation, poll_init() is called by kgdb to initialize
hardware which supports both poll_put_char() and poll_get_char().

It's necessary to enable TXEN bit, otherwise, it will cause hardware fault
and kernel panic when calling imx_poll_put_char().

Generally, if use /dev/ttymxc0 as kgdb console as well as system
console, ttymxc0 is initialized early by system console which does enable
TXEN bit.But when use /dev/ttymxc1 as kgbd console, ttymxc1 is only
initialized by imx_poll_init() cannot enable the TXEN bit, which will
cause kernel panic.
Signed-off-by: NMingrui Ren <jiladahe1997@gmail.com>
Link: https://lore.kernel.org/r/20201202072543.151-1-972931182@qq.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLu Jialin <lujialin4@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/tty/serial/imx.c

@@ -1881,7 +1881,7 @@ static int imx_uart_poll_init(struct uart_port *port)
 	ucr1 |= UCR1_UARTEN;
 	ucr1 &= ~(UCR1_TRDYEN | UCR1_RTSDEN | UCR1_RRDYEN);
 
-	ucr2 |= UCR2_RXEN;
+	ucr2 |= UCR2_RXEN | UCR2_TXEN;
 	ucr2 &= ~UCR2_ATEN;
 
 	imx_uart_writel(sport, ucr1, UCR1);