[fedora-arm] Adding serial console support to extlinux.conf

[Hans de Goede]

Hi All,

I just got a mail from Gerd (in the CC) about some troubles with booting
an ARM device through a serial console.

The problem here is that we do not add a console=... to the append argument
in our extlinux.conf .

One problem is what the ... must be, that one I've already fixed in the
v2014.10 u-boot release by adding support for using uboot env variables
inside the append command in extlinux.conf, so now we can simply append:

console=${console}

But this causes 2 problems for devices which also have a graphical console,
over e.g. hdmi:

1) This sends the kernel boot messages to only the serial port, this can
be easily fixed by instead appending:

console=tty0 console=${console}

2) This will cause first-boot to run on the serial console in text mode,
instead of on the hdmi output

2. is the real deal-breaker here AFAIK. We could fix this by fixing firstboot
to only go serial if there is no framebuffer or some such, or we could fix
this by adding a second extlinux.conf menu entry labelled:

label Fedora-Minimal-armhfp-rawhide-20140731 (...) with serial console

Ideally we would fix first-boot, but we're probably too late in the cycle
for that, so I hope we can at least at the extra entry to the extlinux.conf
on the generated images, if not we will need to document this very clearly,
and serial console users will need to edit extlinux.conf before booting.

Regards,

Hans