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

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Message-ID: <20130712121146.GC17053@arwen.pp.htv.fi>
Date:	Fri, 12 Jul 2013 15:11:46 +0300
From:	Felipe Balbi <balbi@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-serial@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Tony Lindgren <tony@...mide.com>,
	Rajendra Nayak <rnayak@...com>, Felipe Balbi <balbi@...com>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH 2/2] serial: omap: fix wrong context restoration on init

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 ?

oh well...

-- 
balbi

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