linux-kernel - [RFC PATCH] tty/serial: atmel: fix TX path in atmel_console

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Date:   Wed, 15 Mar 2017 16:29:48 +0100
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Richard Genoud <richard.genoud@...il.com>,
        <linux-serial@...r.kernel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        "stable # 4 . 4+" <stable@...r.kernel.org>
Subject: [RFC PATCH] tty/serial: atmel: fix TX path in atmel_console_write()

A side effect of 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA
from transmitting in stop_tx") is that the console can be called with
TX path disabled. Then the system would hang trying to push charecters
out in atmel_console_putchar().

Signed-off-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
Fixes: 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA from transmitting
in stop_tx")
Cc: stable <stable@...r.kernel.org> # 4.4+
---
Hi Richard,

I found this to fix the problem with system hang in my linux-4.4-at91 branch
(in the atmel_console_putchar() waiting loop actually). I'm open to more
insignt.
As we cannot figure out if this bit is set or not, I didn't preserve the
current status...

Regards,

 drivers/tty/serial/atmel_serial.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index dcebb28ffbc4..7372dbdb7a4c 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -2483,6 +2483,9 @@ static void atmel_console_write(struct console *co, const char *s, u_int count)
 	pdc_tx = atmel_uart_readl(port, ATMEL_PDC_PTSR) & ATMEL_PDC_TXTEN;
 	atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
 
+	/* Make sure that tx path is actually able to send characters */
+	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
+
 	uart_console_write(port, s, count, atmel_console_putchar);
 
 	/*
-- 
2.9.0