linux-kernel - Re: [PATCH] pch_dma: Fix channel locking

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Date:	Mon, 27 Jun 2011 16:22:52 +0200
From:	Alexander Stein <alexander.stein@...tec-electronic.com>
To:	Tomoya MORINAGA <tomoya-linux@....okisemi.com>
Cc:	"Wang, Yong Y" <yong.y.wang@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, "Wang, Qi" <qi.wang@...el.com>,
	"toshiharu-linux@....okisemi.com" <toshiharu-linux@....okisemi.com>
Subject: Re: [PATCH] pch_dma: Fix channel locking

Hello,

On Friday 24 June 2011 07:28:12 Tomoya MORINAGA wrote:
> Hi Alexander Stein
> 
> I couldn't see the issue at all.
> 
> (2011/06/23 16:42), Alexander Stein wrote:
> > The close and open is actually needed (I had a separate application for
> > that yesterday).
> 
> Does the above mean that we must delete "close" processing from your
> test program, right ?
> (Modifying like this, I couldn't see the issue)

As you've written below, you used setserial to enable DMA mode. I used my own 
application for that using 2 ioctls.

> > If all is done without closing again, I get the following bug:
> Does the above mean that executing your test program many times whose 2
> "close" are deleted , did you see the issue ?

The issue is only printed once. steps in short:
* Enable DMA
* Send 270 chars

> My steps like below
> Boot Fedora14
> Install DMA driver
> Install pch_uart driver
> Enable DMA (setserial /dev/ttyPCH0 ^low_latency)
> Modifying your test program
>   Delete 2 close() function.
> Compile your test program.
> Execute the tp.
> Execute the tp.
> Execute the tp.
> I couldn't see any error message.

Ok. I have a 2.6.39 kernel with the following patches:
pch_phub: Don't panic if dmi_get_system_info returns NULL
drivers/tty/serial/pch_uart.c: don't oops if dmi_get_system_info returns NULL
pch_uart: Add console support

I need these to get a booting board with console support on pch_uart.
After boot (dma and pch_uart compiled into kernel), I do
* setserial /dev/ttyPCH0 ^low_latency
* ./raise_dma_fault
<- Here I get the message

For the reference the used code for raise_dma_fault:
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/serial.h>
int main(int argc, char *argv[])
{
int fd;
char buf[270];

	fd = open ("/dev/ttyPCH0", O_RDWR);
	write (fd, buf, 270);

	close (fd);
	return 0;
}

Maybe you need to enable CONFIG_TRACE_IRQFLAGS and CONFIG_PROVE_LOCKING 
additionally to see the messages.

Regards,
Alexander
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