Messages in this thread | | | Date | Mon, 30 May 2005 16:38:29 -0600 | From | Jim Ramsay <> | Subject | Bug in 8520.c - port.type not set for serial console |
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I am attempting to get the 8520.c driver's serial console working with a 16550A UART implementation, and have run into what I consider to be a bug: In short, the proper 'port.type' for this serial port is not set until the module init (serial8250_init) is called, so the FCR is set incorrectly during serial8250_console_init for any port type which is different than UNKNOWN.
The exact problem is that the FCR is being set to '0x0' for a port type of 'UNKNOWN', when for my specific 16550A, it should be set to '0xC1' - and this makes my screen fill with empty characters instead of the printk output I need. It appears that after some time (once the kernel actually calls serial8250_init) the problem clears up, but I still lose a large section of the output before this point.
The proper flags are sitting there in the uart_config array for the proper type, and this type is properly deduced by the 'autoconfig' routine that eventually gets called by serial8250_init. The problem is that the autoconfig is isn't called by serial8250_console_init which of course happens much earlier than serial8250_init.
I have a workaround that works for me, telling the serial8250_set_termios() routine to only set the FCR if the type is not UNKNOWN, changing if (up->port.type != PORT_16750 ) { to if (up->port.type != PORT_16750 && up->port.type != PORT_UNKNOWN) {
This will leave the FCR at whatever it was at boot time, which for me is correct.
Would this be a "good enough" fix in general, or would there be a better way of doing this?
I suppose the other way would be to duplicate some of what serial8250_init does (like call 'autoconfig') in serial8250_console_init, but I haven't tried this yet... maybe it depends on too much kernel magic to be called as early as 'console_init'?
Any suggestions on the best way to fix this would be great, I'd be happy to develop this more, test a bit, and submit a patch.
-- Jim Ramsay "Me fail English? That's unpossible!" - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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