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


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