On Fri, Jul 12, 2013 at 03:11:46PM +0300, Felipe Balbi wrote:

hi,

On Fri, Jul 12, 2013 at 02:55:42PM +0300, Grygorii Strashko wrote:

quoted

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 <redacted>
CC: Felipe Balbi <redacted>
CC: Kevin Hilman <redacted>

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;

you really think adding this sort of bool flag is the best thing we can
do ? Something which will, quite likely, spread through every single
driver ?

I agree, that's not ok, please fix this up "properly" somehow.

thanks,

greg k-h