On Fri, 2015-01-02 at 22:13 +0100, Karsten Merker wrote:
> On Fri, Jan 02, 2015 at 02:51:18PM +0100, Karsten Merker wrote:
> > On Fri, Jan 02, 2015 at 10:46:37AM +0000, Ian Campbell wrote:
>
> > > BTW our kernel now supports the /chosen/stdout-path property in fdt and
> > > will automatically put a console on it.
> >
> > Just to make sure that I understand that correctly: with the
> > u-boot and kernel versions currently in Jessie, there is no need
> > to ever pass a console parameter to the kernel on any platform?
> > Or is this something that was introduced after the u-boot v2014-10
> > release in Jessie?
>
> Hello,
>
> I have in the meantime run some tests and this functionality does
> not seem to be available with the current versions in Jessie. If
> I do not explicitly set bootargs to include a console parameter,
> I get no console output, although u-boot has a valid ${console}.
The support is in linux 3.16.7-ckt2-1, which is in Jessie right now but
I don't know if it is in the kernel used by the current d-i, probably
not since that is in the process of being updated.
> Even if we cannot use that functionality at the moment, I am
> interested in how it works: does u-boot just copy the content of
> ${console} into the /chosen/stdout-path property, or is there
> some additional mechanism to hand over a baudrate for serial
> connections to the kernel?
I think it comes from the fdt, u-boot needn't be involved at all,
although it could be if the platform demanded it.
The stdout-path property is a device-tree path to the device to use, so
it is e.g. /smb/motherboard/iofpga@3,00000000/uart@090000 (or an
equivalent alias), it's not e.g. ttyS0 or ttyAMA0 etc.
Ian.
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