[PATCH 2/2] serial: omap: fix wrong context restoration on init

[Grygorii Strashko <grygorii.strashko@ti.com>]

Since commit a630fbf "serial: omap: Fix device tree based PM runtime"
the OMAP serial driver will always try to restore its context in
serial_omap_runtime_resume(). But the problem is that during driver
initialization the UART context is not ready yet and, as result, first
call to pm_runtime_get*() will cause UART register overwriting by all
zeros. This causes Kernel boot hang in case if "earlyprintk" feature is
enabled at least [1].

Unfortunately, there is no exact place in driver now where we can
determine that UART context is ready - most of registers configured in
serial_omap_set_termios(), but some of them in other places.
More over, even if PM runtime will be disabled (blocked) during OMAP
serial driver probe() execution [2],[3] it will fix only console UART,
but context of other UARTs will be overwriting by all zeros during first
access to the corresponding UART.

To fix this issue:
- introduce additional "initialized" flag and update PM runtime callback
to do nothing if its not set. Set "initialized" at the end of probe().
- read current UART registers configuration in probe and use it by
default.

[1] http://www.spinics.net/lists/arm-kernel/msg256828.html
[2] http://www.spinics.net/lists/arm-kernel/msg258062.html
[3] http://www.spinics.net/lists/arm-kernel/msg258040.html

CC: Tony Lindgren <tony@atomide.com>
CC: Rajendra Nayak <rnayak@ti.com>
CC: Felipe Balbi <balbi@ti.com>
CC: Kevin Hilman <khilman@linaro.org>

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
---
tested on OMAP4 SDP with and without earlyprintk enabled.
 drivers/tty/serial/omap-serial.c |   27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index f39bf0c..e1e9667 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -162,6 +162,7 @@ struct uart_omap_port {
 	struct work_struct	qos_work;
 	struct pinctrl		*pins;
 	bool			is_suspending;
+	bool			initialized;
 };
 
 #define to_uart_omap_port(p)	((container_of((p), struct uart_omap_port, port)))
@@ -1395,6 +1396,19 @@ static struct omap_uart_port_info *of_get_uart_port_info(struct device *dev)
 	return omap_up_info;
 }
 
+static void serial_omap_save_context_def(struct uart_omap_port *up)
+{
+	up->dll = serial_in(up, UART_DLL);
+	up->dlh = serial_in(up, UART_DLM);
+	up->ier = serial_in(up, UART_IER);
+	up->fcr = serial_in(up, UART_FCR);
+	up->mcr = serial_in(up, UART_MCR);
+	up->scr = serial_in(up, UART_OMAP_SCR);
+	up->efr = serial_in(up, UART_EFR);
+	up->lcr = serial_in(up, UART_LCR);
+	up->mdr1 = serial_in(up, UART_OMAP_MDR1);
+}
+
 static int serial_omap_probe(struct platform_device *pdev)
 {
 	struct uart_omap_port	*up;
@@ -1518,10 +1532,14 @@ static int serial_omap_probe(struct platform_device *pdev)
 	ui[up->port.line] = up;
 	serial_omap_add_console_port(up);
 
+	serial_omap_save_context_def(up);
+
 	ret = uart_add_one_port(&serial_omap_reg, &up->port);
 	if (ret != 0)
 		goto err_add_port;
 
+	up->initialized = true;
+
 	pm_runtime_mark_last_busy(up->dev);
 	pm_runtime_put_autosuspend(up->dev);
 	return 0;
@@ -1619,6 +1637,9 @@ static int serial_omap_runtime_suspend(struct device *dev)
 	if (!up)
 		return -EINVAL;
 
+	if (!up->initialized)
+		return 0;
+
 	/*
 	* When using 'no_console_suspend', the console UART must not be
 	* suspended. Since driver suspend is managed by runtime suspend,
@@ -1652,8 +1673,12 @@ static int serial_omap_runtime_suspend(struct device *dev)
 static int serial_omap_runtime_resume(struct device *dev)
 {
 	struct uart_omap_port *up = dev_get_drvdata(dev);
+	int loss_cnt;
+
+	if (!up->initialized)
+		return 0;
 
-	int loss_cnt = serial_omap_get_context_loss_count(up);
+	loss_cnt = serial_omap_get_context_loss_count(up);
 
 	if (loss_cnt < 0) {
 		dev_dbg(dev, "serial_omap_get_context_loss_count failed : %d\n",
-- 
1.7.9.5