linux-kernel - [PATCH 06/10] tty: xuartps: Force enable the UART in xuartps_console

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Date:	Thu, 17 Oct 2013 14:08:09 -0700
From:	Soren Brinkmann <soren.brinkmann@...inx.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Michal Simek <michal.simek@...inx.com>
Cc:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Lars-Peter Clausen <lars@...afoo.de>,
	John Linn <john.linn@...inx.com>,
	Soren Brinkmann <soren.brinkmann@...inx.com>
Subject: [PATCH 06/10] tty: xuartps: Force enable the UART in xuartps_console_write

From: Lars-Peter Clausen <lars@...afoo.de>

It is possible that under certain circumstances xuartps_console_write is entered
while the UART disabled. When this happens the code will busy loop in
xuartps_console_putchar, since the character is never written and the TXEMPTY
flag is never set. The result is a system lockup. This patch force enables the
UART for the duration of xuartps_console_write to avoid this.

Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
Signed-off-by: John Linn <john.linn@...inx.com>
Signed-off-by: Michal Simek <michal.simek@...inx.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
---
Squashed from these original patches:
	tty: xuartps: Force enable the UART in xuartps_console_write

	It is possible that under certain circumstances xuartps_console_write is entered
	while the UART disabled. When this happens the code will busy loop in
	xuartps_console_putchar, since the character is never written and the TXEMPTY
	flag is never set. The result is a system lockup. This patch force enables the
	UART for the duration of xuartps_console_write to avoid this.

	Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>

and

	tty: xuartps: Fix bad register write in console_write

	The commit:
	serial: xilinx_uartps: Force enable the UART in xuartps_console_write
	(sha1: d21aec67c1c782314d20b3d619e76cf8aae593dc)
	caused  a new bug as the write to the control register had
	the offset and the value to write reversed.

	Reported-by: Jason Andrews <jasona@...ence.com>
	Signed-off-by: John Linn <john.linn@...inx.com>
	Signed-off-by: Michal Simek <michal.simek@...inx.com>
---
 drivers/tty/serial/xilinx_uartps.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 6e8ec6e9d5a2..fdc739b55eb3 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -953,7 +953,7 @@ static void xuartps_console_write(struct console *co, const char *s,
 {
 	struct uart_port *port = &xuartps_port[co->index];
 	unsigned long flags;
-	unsigned int imr;
+	unsigned int imr, ctrl;
 	int locked = 1;
 
 	if (oops_in_progress)
@@ -965,9 +965,19 @@ static void xuartps_console_write(struct console *co, const char *s,
 	imr = xuartps_readl(XUARTPS_IMR_OFFSET);
 	xuartps_writel(imr, XUARTPS_IDR_OFFSET);
 
+	/*
+	 * Make sure that the tx part is enabled. Set the TX enable bit and
+	 * clear the TX disable bit to enable the transmitter.
+	 */
+	ctrl = xuartps_readl(XUARTPS_CR_OFFSET);
+	xuartps_writel((ctrl & ~XUARTPS_CR_TX_DIS) | XUARTPS_CR_TX_EN,
+		XUARTPS_CR_OFFSET);
+
 	uart_console_write(port, s, count, xuartps_console_putchar);
 	xuartps_console_wait_tx(port);
 
+	xuartps_writel(ctrl, XUARTPS_CR_OFFSET);
+
 	/* restore interrupt state, it seems like there may be a h/w bug
 	 * in that the interrupt enable register should not need to be
 	 * written based on the data sheet
-- 
1.8.4.1

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