Bug#783074: flash-kernel: improvements to uboot-generic bootscript
On Sun, 2015-06-07 at 09:36 -0700, Vagrant Cascadian wrote:
> On 2015-06-07, Ian Campbell wrote:
> > On Mon, 2015-05-04 at 12:01 -0700, Vagrant Cascadian wrote:
> >> I can confirm that wandboard, cubox-i and hummingboard all default to
> >> console=ttymxc0, and several other boards by grepping through u-boot's
> >> include/configs. Some actually do "setenv bootargs
> >> console=ttymxc0,${baudrate}" before their various boot commands.
> >>
> >> If you prefer a more specific comment, maybe "Workaround lack of
> >> baudrate included with console on various iMX systems (e.g. wandboard,
> >> cubox-i, hummingboard)." An exhaustive list might prove more trouble
> >> than it's worth. :)
> >
> > For sure!
> >
> > I was thinking about this some more and it occurred to me that
> > console=ttymxc0 (or indeed any console=ttyFOO) ought really to be
> > inheriting the existing baud rate etc settings from the bootloader and
> > Just Work(tm).
>
> It defaults to 9600 baud (u-boot defaults to 115200), and consequently
> the serial console looks like gibberish.
>
>
> > That lead me to drivers/tty/serial/imx.c:imx_console_get_options() in
> > the kernel which is called if no options are given.
> >
> > That code has been there since the beginning of git history. Did you try
> > with just console=ttymxc0 and it didn't work? (Sorry if this is a silly
> > question, I think many people don't realise the baud etc is optional so
> > it never gets tried).
> >
> > If you've tried without and it doesn't work then either that code isn't
> > called when I think, or it is broken. In either case I'm not too
> > inclined to investigate further than "does console=ttymxc0 work" and if
> > not then apply that bit of the patch.
>
> I haven't investigated the kernel code, but my experience shows that
> without specifying the baud rate it defaults to 9600.
>
> 9600 baud seems a bit antiquated at this point... :)
Absolutely. I really think you've found a kernel bug though, the code
looks very much like it is trying to read the baud rate from the HW if
it is enabled. I can't see by inspection why it is not working. Maybe
u-boot disables the uart before booting the kernel?
Ian.
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