Discussion:
[ORLinux] serial problem in 3.9
Henrik Nordström
2013-06-26 08:51:17 UTC
Permalink
Seems something is broken with the serial support in 3.9 and later.
Tested openrisc-3.9 branch form Jonas repository and current mainline as
of yesterday with same symptom. The exact same kernel config & dts works
fine on 3.8 and earlier.

Running in or1ksim works fine, but on two different FPGA boards the
serial port becomes silent once fully configured. The early bootconsole
do work, and boot continues fine up to userspace if keep_bootcon is used
and serial0 is disabled in the dts (i.e. disabling the full serial
driver, only using simple polled bootcon driver).

To keep things simple the tested kernel config & dts is the same as for
or1ksim except for clock frequency.

Regards
Henrik
Henrik Nordström
2013-07-03 23:38:26 UTC
Permalink
Post by Henrik Nordström
Seems something is broken with the serial support in 3.9 and later.
Tested openrisc-3.9 branch form Jonas repository and current mainline as
of yesterday with same symptom. The exact same kernel config & dts works
fine on 3.8 and earlier.
Stefan Kristiansson have reproduced this on de0_nano and his atlyst
board. But it did not show up for him in a verilator simulation.

It seems to be something related to the switch from 8250_early to
8250_core drivers. If earlycon is NOT used (console=ttyS0,115200) then
the console works.

A diff of linux-3.8 -> 3.9 drivers/tty/serial/8250/ shows nothing
obvious.

Investigation still pending. Don't know if it's rtl "hardware" bug or
software bug..

Regards
Henrik
Henrik Nordström
2013-07-04 02:05:18 UTC
Permalink
Problem found, and it's a generic kernel bug.

Patch filed at https://patchwork.kernel.org/patch/2821521/

A workaround is to use
earlycon=uart,... console=ttyS0,115200
intead of
console=uart,...

Regards
Henrik

Loading...