linux-kernel - Re: [PATCH 2/2] serial: omap: fix wrong context restoration on init

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Date:	Fri, 26 Jul 2013 16:00:51 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Felipe Balbi <balbi@...com>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	linux-serial@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	Rajendra Nayak <rnayak@...com>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH 2/2] serial: omap: fix wrong context restoration on init

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:
> > 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@...mide.com>
> > CC: Rajendra Nayak <rnayak@...com>
> > CC: Felipe Balbi <balbi@...com>
> > CC: Kevin Hilman <khilman@...aro.org>
> > 
> > Signed-off-by: Grygorii Strashko <grygorii.strashko@...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
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