Occasional fail to initiate resume by incoming call, easy workaround proposed

Paul Fertser fercerpav at gmail.com
Mon Feb 9 14:21:14 CET 2009


Not exactly kernel issue, but since it is very low-level and affects
all distributions, i hope this ML is appropriate enough.

Short summary:

Calypso will not generate any interrupt until it sees CTS_MODEM fall
for the first time after powering on. That leads to inability to
trigger a first resume by calling or sending an SMS after turning on
GSM and suspending.

Userspace workaround:

After the Calypso is powered on, do "echo 1 >
/sys/bus/platform/devices/neo1973-pm-gsm.0/flowcontrolled; echo 0 >

Long story:

For quite some time i wondered why sometimes my FR doesn't resume on
incoming call while pressing power button works perfectly.

Joerg was extremely helpful on IRC and spent considerable time
discussing all kinds of wild guesses, ways to reproduce, possible
races, irq handling techniques, testpoints access etc. Without his
help i'd given up long time ago. Werner, mwester, lindi and Kensan
also took part in discussions and gave plenty of good hints.

Finally a reproducible testcase was constructed and with a help of
Werner's gpio tool it became obvious how the interrupt line works and
why it fails for the first time.

Calypso is supposed to generate interrupt (via IO1 line, connected to
EINT1/GPF1 at SoC side) in every case when it has some data to send to
SoC but CTS_MODEM (NRTS0/GPH1) prohibits sending. It does that by
pulling the line up and pulls the line down after CTS_MODEM is
de-asserted (pulled down). The kernel is configured to react on edge
rise, so the interrupt is generated and if device is suspended, resume
is initiated.

The problem can be seen right after powering on the modem because it
doesn't pull the IRQ line low on init and therefore it is unable to
generate rise. Joerg believes that it's a firmware bug and should be
fixed in the next version. If CTS_MODEM fall is somehow generated once
(with sysfs node or suspending and resuming by other means), calypso
finally pulls the line low and after that works as expected.

Sounds easy, doesn't it? ;)

Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software!
mailto:fercerpav at gmail.com

More information about the openmoko-kernel mailing list