Messages in this thread | | | Date | Wed, 4 Jan 2012 12:53:10 -0800 | From | Greg KH <> | Subject | Re: UV serial regression since 2.6.36 |
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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
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