RE: Problem of concurrency in arch/ppc/8260_io/uart.c

Yes, I have seen this problem when I have a lot of printks from interrupt
context on my 8255 board using an SCC as the console. It's been on my list
for awhile but I haven't done anything about it yet. I think the easy
approach would be to disable interrupts when manipulating the buffer
descriptors (in fact, there are comments in the driver that make me suspect
this used to be the done). But there would be a performance hit for this.
Anyone got a more elegant suggestion?

Dean Dayton

-----Original Message-----
From: Jean-Denis Boyer [mailto:jdboyer@mediatrix.com]
Sent: Thursday, March 06, 2003 4:39 PM
To: Linux PPC embedded
Subject: Problem of concurrency in arch/ppc/8260_io/uart.c



I have a problem of concurrency on my 8250 based custom
board. I'm using kernel 2.4.19, and the output on the serial
port goes crappy.

It seems to appear when printk is called from interrupt
context, while a user mode process is writing to stdout.

I wrote a user mode program + a kernel module to reproduce
the problem. The kernel module starts a timer that calls
printk (34 chars) each 100ms. The user mode program performs
a while(1) printf(...); That combination almost immediatly
mess the serial driver, that begins to output characters in
an unpredictable order, until we reboot. It never crashes,
however, but it is annoying.

Has anyone encoutered that problem?
or has any suggestion before I go further?
or wish to have the test program to give it a try?

Thanks,
--------------------------------------------
 Jean-Denis Boyer, B.Eng., Technical Leader
 Mediatrix Telecom Inc.
 4229 Garlock Street
 Sherbrooke (Québec)
 J1L 2C8  CANADA
 (819)829-8749 x241
--------------------------------------------

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