ttySx probing

ttySx probing

[Renaud Barbier]

Hello,
I have a Freescale P1014 custom board with the UARTs connected as follows:
UART0 -> BMM (Board management device connected to sensors) ttyS0 115200
bauds
UART1 -> Not used. Disable in the device tree.
UART2 -> Console. ttyS1 - 9600 bauds
UART3 -> Not used. ttyS2

I am using Linux 3.14
The bootargs specifices console=ttyS1,9600n8
I have two issues:

When booting a few lines of garbage characters are printed when ttyS0 is
probed.
serialªrÒÒ¢ÑåMÅÑyS0 at MMIO 0xffe04500 (irq = 42, base_baud = 20833333)
is a 165
ÑÑ55%=ÁááÁÑÝÁÁÑ¡¥ÉÅÉõÑɱõ±
ÍÍ}½¹Íͽ¹Íͽ±mÕÕѹ¹ loaded
±5)½½Ñ½¹Íͽ±mÕÕÍÍ
5)½½ÑÑ
...
Later the system reached the prompt.

These type of character also appears when setting UART0 to  9600/115200
bauds in the boot loader or not programming the speed at  all.

This does not happen when  UART0 is disabled in the device tree.

I do not understand why Linux would attempt to use ttyS0 when the
console is specified as ttyS1. Is there a way to prevent this behaviour?


Next, if I do not program  a baud rate in UART0 from the boot loader and
use for instance the command stty -F /dev/ttyS0. There is an interrupt
flood and Linux hangs. The same happen when using the tools accessing
the BMM. No character seems to be transmitted or received.
Note that I need to spent for time gathering data on this issue.


I am looking for a way to solve the first issue. I was thinking to get
ttyS1 (UART2) to be probed first and see whether that would prevent
these characters from being printed or any other possible solution to
test. Though, I am  not sure how this can be accomplished after looking
at boot argument controlling console access or changing the device tree.

I would appreciate any suggestions.

Cheers,
Renaud

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