[PATCH] arm: kirkwood: Enable uart0 dm-pre-reloc for Kirkwood boards

[Pali Rohár]

On Wednesday 01 February 2023 09:17:15 Michael Walle wrote:
> > > > When DM_SERIAL is enabled, the device-tree property dm-pre-reloc is
> > > > required to boot over UART with kwboot. Enable this in a Kirkwood
> > > > common u-boot dtsi.
> > > 
> > > My (dev) board unfortunately, have a bootloader which can't boot over
> > > serial.
> > 
> > This is feature of Marvell BootROM and does not require any special from
> > Bootloader. So you should be able to boot over UART (if you have
> > accessible pins).
> 
> I know, but there are known versions ob the bootrom where uart boot
> isn't supported (correctly).

I heard about it... maybe it is a bug in client software (kwboot)? I do
not have such board if you are interested in it I could try to send some
details how to debug it.

> I also have another board which can boot
> over uart. But thats in daily use ;)
> 
> > > Could you elaborate that a bit more? Why is this required for
> > > uart boot? kwboot will talk with the bootrom why does u-boot need
> > > anything? Or will there just be no output until the uart is
> > > initialized?
> > 
> > On mvebu/armada boards this dm-pre-reloc is required to ensure that DT
> > nodes are present in SPL DTB file. Otherwise build process drop all
> > non-pre-realoc nodes from SPL version of DTB file. And because SPL use
> > DM serial, it is required to have uart DT nodes in DTB file. Btw, same
> > problem is with SPI in SPL.
> > 
> > But... kirkwood does not use SPL, so I do not know what is reason for
> > this here.
> 
> Yes thats what puzzled me, too.
> 
> > > >
> > > > Signed-off-by: Tony Dinh <mibodhi at gmail.com>
> > > > ---
> > > >
> > > >  arch/arm/dts/kirkwood-u-boot.dtsi | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >  create mode 100644 arch/arm/dts/kirkwood-u-boot.dtsi
> > > 
> > > Is this new? AFAIK only <boardname>-u-boot.dtsi is included
> > > automatically.
> > 
> > It is not new, Tom wrote about it quite ago:
> > https://lore.kernel.org/u-boot/20220802121113.GG1146598@bill-the-cat/
> 
> Thats relatively new for someone not following the u-boot
> development that closely ;) Thanks for the pointer.
> 
> -michael
>