Re: UV serial regression since 2.6.36

[Greg KH <gregkh@suse.de>]

On Wed, Jan 04, 2012 at 07:41:47PM +0100, Jiri Slaby wrote:
> On 12/06/2011 11:34 PM, Jiri Slaby wrote:
> > Hi,
> > 
> > In short, the issue causes serial port traffic to stop after some time
> > on UV machines. Only when serial is used as a console. It worked
> > perfectly with 2.6.32. It's a standard 16550 on 0x3f8 (well, it's
> > emulated to be at that port). Also in the PNP subsys.
> > 
> > To reproduce that 'debug' kernel parameter must not be used.
> > 
> > The root cause seems to be that the serial "chip" there has problems
> > with interrupts. It generates some but doesn't indicate it's the source
> > or somebody clears it (NOINT is set). And when it is supposed to
> > generate one (on THRE), it does not. So there are bytes in the TX buffer
> > which are never sent. Until the port is kicked e.g. by "echo h >
> > /proc/sysrq-trigger".
> > 
> > The unhandled interrupts were always an issue, but somehow hidden. It
> > became a real problem with patches post 2.6.32.
> > 
> > I bisected it to these two commits _together_:
> > 
> > commit 3f582b8c11014e4ce310d9839fb335164195333f
> > Author: Arnd Bergmann <arnd@arndb.de>
> > Date:   Tue Jun 29 22:31:40 2010 +0200
> > 
> >     serial: fix termios settings in open
> > 
> > AND
> > 
> > commit 74c2107759dc6efaa1b9127014be58a742a1e7ac
> > Author: Alan Cox <alan@linux.intel.com>
> > Date:   Tue Jun 1 22:53:00 2010 +0200
> > 
> >     serial: Use block_til_ready helper
> > 
> > Those reverted on the top of 2.6.37 makes it work again. Those reverted
> > on the top of 3.0 plus mine 3 reverted which removed update_set_termios
> > completely makes it work again.
> > 
> > I didn't look closely to why those patches are causing that. Like
> > c_cflag copy in uart_update_termios and "tty->termios->c_cflag & CBAUD"
> > test in tty_port_block_til_ready don't look good to me...
> 
> My vacation is over. I suppose you haven't had a chance to take a look
> into the regression? (Just in case any of you is looking into that right
> now to not duplicate the effort.)

I haven't, sorry, as I was on vacation as well.

greg k-h