Bug 170554 – gentoo-sources-2.6.19-r5 - Specialix SX board does not work any more

• Product: Gentoo Linux
• Status: RESOLVED FIXED

[Description Graham Murray 2007-03-12 11:36:03 UTC]

When running the kernel from gentoo-sources-2.6.17-r7, the applications using the Specialix SX Multiport serial card work as expected. After updating the system to kernel 2.6.19-r5 the applications do not work. The messages log shows lines like
"Mar 12 10:08:06 dev1 sx: unsupported baud rate: 1200342922." and the application does not see incoming characters. 

If I boot using kernel 2.6.17-r7, everything works. If I boot from 2.6.19-r5 I get the above, and if (as an experiment) I try the unstable 2.6.0-gentoo kernel, it does not even detect the card.

I have tried configuring the driver as built into the kernel and as a module. I have tried installing the unstable linux-headers-2.6.19.2-r2 and rebuilding glibc and the applications. But the effect is the same - it all works if I boot 2.6.17-r7 but not 2.6.19-r5.

Portage 2.1.2-r9 (default-linux/x86/2006.1/server, gcc-4.1.1, glibc-2.5-r0, 2.6.19-gentoo-r5 i686)
=================================================================
System uname: 2.6.19-gentoo-r5 i686 Intel(R) Xeon(TM) CPU 3.20GHz
Gentoo Base System release 1.12.9
Timestamp of tree: Tue, 06 Mar 2007 13:00:01 +0000
distcc 2.18.3 i686-pc-linux-gnu (protocols 1 and 2) (default port 3632) [disabled]
ccache version 2.3 [disabled]
dev-lang/python:     2.4.3-r4
dev-python/pycrypto: 2.0.1-r5
dev-util/ccache:     2.3
sys-apps/sandbox:    1.2.17
sys-devel/autoconf:  2.13, 2.61
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10
sys-devel/binutils:  2.16.1-r3
sys-devel/gcc-config: 1.3.14
sys-devel/libtool:   1.5.22
virtual/os-headers:  2.6.19.2-r2
ACCEPT_KEYWORDS="x86"
AUTOCLEAN="yes"
CBUILD="i686-pc-linux-gnu"
CFLAGS="-O2 -pipe -march=pentium4 -ggdb"
CHOST="i686-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/share/X11/xkb /usr/share/config"
CONFIG_PROTECT_MASK="/etc/env.d /etc/gconf /etc/revdep-rebuild /etc/terminfo"
CXXFLAGS="-O2 -pipe -march=pentium4 -ggdb"
DISTDIR="/usr/portage/distfiles"
FEATURES="autoconfig distlocks getbinpkg metadata-transfer sandbox sfperms splitdebug strict"
GENTOO_MIRRORS="http://distfiles.gentoo.org http://distro.ibiblio.org/pub/linux/distributions/gentoo"
LANG="en_GB.UTF-8"
LC_ALL="en_GB.UTF-8"
PKGDIR="/usr/portage/packages"
PORTAGE_RSYNC_EXTRA_OPTS="--exclude-from=/etc/portage/rsync_excludes"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
SYNC="rsync://rsync.webwayone.co.uk/gentoo-portage"
USE="apache2 berkdb bitmap-fonts bzip2 cli cracklib crypt doc examples fortran gdbm gpm iconv ipv6 isdnlog libg++ logrotate mailwrapper midi mmx ncurses nls nptl nptlonly pam pcre perl postgres ppds pppd python readline reflection session snmp spl sse sse2 ssl symlink tcpd threads truetype truetype-fonts type1-fonts unicode x86 xml xorg zlib" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1 emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file hooks iec958 ioplug ladspa lfloat linear meter mulaw multi null plug rate route share shm softvol" ELIBC="glibc" INPUT_DEVICES="keyboard mouse evdev" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" USERLAND="GNU" VIDEO_CARDS="radeon fbdev"
Unset:  CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LDFLAGS, LINGUAS, MAKEOPTS, PORTDIR_OVERLAY

[Comment 1 Graham Murray 2007-03-12 11:36:49 UTC]

Created attachment 113057 [details]
Kernel config for working 2.6.17-r7

[Comment 2 Graham Murray 2007-03-12 11:37:37 UTC]

Created attachment 113058 [details]
Kernel config for failing 2.6.19-r5

[Comment 3 Graham Murray 2007-03-13 09:35:12 UTC]

Further investigation has shown

1) The same problem occurs with vanilla-sources-2.6.19-r5

2) The ports are actually working but at 9600bps instead of the configured 115200bps. Strace of one of the applications shows that the IOCTL is called with a B115200 value and that the syscall returns a 0 result code and stty shows them as configured for 115200.

[Comment 4 Daniel Drake (RETIRED) 2007-03-13 12:18:17 UTC]

If you're really keen and have some time on your hands you can track down the exact commit which introduced the bug with:
http://www.reactivated.net/weblog/archives/2006/01/using-git-bisect-to-find-buggy-kernel-patches/

It's actually fairly obvious that one commit from a certain small group of patches would have added this bug (SX had a series of cleanups merged for this release), but I don't have time to start formatting the patches right now.

[Comment 5 Graham Murray 2007-03-13 14:16:22 UTC]

With a bit of looking around and judicious use of printk, I think I have found the problem in gentoo-sources-2.6.19-r5.

In drivers/char/generic_serial.c in routine gs_set_termios(), it calls tty_get_baud_rate() and then uses the return value to index into the gs_baudrates array. The problem being that tty_get_baud_rate() returns the actual baud rate but gs_set_termios() is treating the result as an index to the baud rate table.

Commenting out the line
   baudrate = gs_baudrates[baudrate];
and just using the result of tty_get_baud_rate() seems to have fixed the problem and all is working properly now.

[Comment 6 Daniel Drake (RETIRED) 2007-03-24 18:08:32 UTC]

Thanks for digging into this, that is indeed the correct fix.

[Comment 7 Daniel Drake (RETIRED) 2007-03-25 19:49:42 UTC]

patch accepted upstream

[Comment 8 Daniel Drake (RETIRED) 2007-04-07 21:36:03 UTC]

fixed in Linux 2.6.20.5 / genpatches-2.6.20-6 / gentoo-sources-2.6.20-r5