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SubjectLinux kernel 2.4.19 failure to access a serial port
Summary: In an i586 system with two serial ports and a modem,
Linux fails to access the modem

Slight expansion: A system with two serial ports on ttyS0 and ttyS1
and a hardware modem on ttyS2 was not serviced properly in kernel
2.4.19 and some earlier ones. The modem at ttyS2 was fairly well
ignored. The interrupt requests used were ttyS0:irq4 ttyS1:irq3
ttyS2:irq10

Temporary fix:
In drivers/char/serial.c at the directive "#ifdef CONFIG_PCI"
the assumption is made that interrupt requests are shared and
there are more than four serial ports. That is not necessarily
true, and the directives defeat the options set in configuration.
The solution here was to comment out #define CONFIG_SERIAL_SHARE_IRQ
and CONFIG_SERIAL_MANY_PORTS and recompile.

#ifdef CONFIG_PCI
#define ENABLE_SERIAL_PCI
/*** Commented out to allow unshared IRQ's on ttyS0-ttyS3
#ifndef CONFIG_SERIAL_SHARE_IRQ
#define CONFIG_SERIAL_SHARE_IRQ
#endif
#ifndef CONFIG_SERIAL_MANY_PORTS
#define CONFIG_SERIAL_MANY_PORTS
#endif
***/
#endif

It seems a more sophisticated judgement needs to be made, and
perhaps simply following the directions of the configurer would be
advisable, in that these two items are made specifically available
in configuration, and should not be silently bypassed.

Note: I have been informed the mailer here does not break lines as
shown on the screen. I hope this message turned out better. It is
purposely reposted so the viewer doesn't have to deal with the
unbroken line version






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