linux-kernel - Re: [PATCH v4 08/11] tty: add pruss SUART driver

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Date:	Tue, 10 May 2011 11:47:02 +0530
From:	"Subhasish Ghosh" <subhasish@...tralsolutions.com>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Cc:	<davinci-linux-open-source@...ux.davincidsp.com>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	<linux-arm-kernel@...ts.infradead.org>, <m-watkins@...com>,
	<nsekhar@...com>, <sachi@...tralsolutions.com>,
	"Andrew Morton \(commit_signer:1/4=25%\)" <akpm@...ux-foundation.org>,
	"Randy Dunlap \(commit_signer:1/4=25%\)" <randy.dunlap@...cle.com>,
	"open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 08/11] tty: add pruss SUART driver

Hi Alan,

>> >> I then modified this function to as follows and the error is not 
>> >> observed
>> >> anymore.
>> >
>> > That looks like you are somehow calling uart_carrier_raised somewhere
>> > with interrupts disabled ?
>> >
>> I am not calling this function in my driver atall, this is getting called 
>> by
>> tty_port.c
>
> Can you verify the status of the interrupt flags at the point that
> routine is called in your code and get a backtrace of the path. It
> should never be gettng called with interrupts off, and if it is we need
> to know what the path is. Otherwise that code change would imply a bug
> in the core code for the platform which seems less likely.

Here is the back trace:

root@...go:~# ------------[ cut here ]------------
WARNING: at drivers/tty/serial/pruss_suart.c:295 
uart_carrier_raised+0x2c/0x74()
Modules linked in: pruss_uart
[<c002e888>] (unwind_backtrace+0x0/0xec) from [<c003e400>] 
(warn_slowpath_common+0x4c/0x64)
[<c003e400>] (warn_slowpath_common+0x4c/0x64) from [<c003e430>] 
(warn_slowpath_null+0x18/0x1c)
[<c003e430>] (warn_slowpath_null+0x18/0x1c) from [<c0190744>] 
(uart_carrier_raised+0x2c/0x74)
[<c0190744>] (uart_carrier_raised+0x2c/0x74) from [<c0182b84>] 
(tty_port_carrier_raised+0x1c/0x20)
[<c0182b84>] (tty_port_carrier_raised+0x1c/0x20) from [<c0183174>] 
(tty_port_block_til_ready+0x254/0x328)
[<c0183174>] (tty_port_block_til_ready+0x254/0x328) from [<c017d3ac>] 
(tty_open+0x310/0x478)
[<c017d3ac>] (tty_open+0x310/0x478) from [<c009f5d8>] 
(chrdev_open+0x1b4/0x1d0)
[<c009f5d8>] (chrdev_open+0x1b4/0x1d0) from [<c009ae34>] 
(__dentry_open+0x170/0x27c)
[<c009ae34>] (__dentry_open+0x170/0x27c) from [<c009b008>] 
(nameidata_to_filp+0x50/0x5c)
[<c009b008>] (nameidata_to_filp+0x50/0x5c) from [<c00a70e0>] 
(finish_open+0x90/0x17c)
[<c00a70e0>] (finish_open+0x90/0x17c) from [<c00a8fa4>] 
(do_filp_open+0x23c/0x520)
[<c00a8fa4>] (do_filp_open+0x23c/0x520) from [<c009ac0c>] 
(do_sys_open+0x58/0xe4)
[<c009ac0c>] (do_sys_open+0x58/0xe4) from [<c0029fa0>] 
(ret_fast_syscall+0x0/0x2c)

flags ---> 0xA0000013


This is how I generated the trace:

static void pruss_suart_enable_ms(struct uart_port *port)
{
        struct omapl_pru_suart *soft_uart =
            container_of(port, struct omapl_pru_suart, port[port->line]);
        struct device *dev = soft_uart->dev;

        WARN_ON(1);
        dev_dbg(dev, "modem control timer not supported\n");
} 

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