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

[Tony Dinh]

Hi all,

On Thu, Feb 2, 2023 at 10:04 AM Pali Rohár <pali at kernel.org> wrote:
>
> On Wednesday 01 February 2023 13:13:16 Tony Dinh wrote:
> > Hi all,
> >
> > On Wed, Feb 1, 2023 at 11:05 AM Pali Rohár <pali at kernel.org> wrote:
> > >
> > > 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.
> >
> > The Kirkwood SoCs came with different BootROM versions. Version 1.1
> > cannot be booted over UART, but version 1.2  can. I think there must
> > be a bug in the BootROM 1.1. The older Kirkwood such as Sheevaplug,
> > Dockstar, iConnect boards come with BootROM 1.1. Later version of
> > Sheevaplug, GoFlex Home, GoFlex Net, Dreamplug, Pogoplug V4, Zyxel
> > NSA310S, NSA320, NSA325 come with BootROM 1.2. So even though it is
> > the same SoC, eg. 6281, they are actually produced at a different time
> > and have different BootROM versions.
>
> There are always multiple revisions of the same SoC. So it is possible
> that something was broken on first revision of 88F6281 and in next
> revision was updated BootROM with some fixes. Revision is written on
> package label and for Armada SoCs it is available also in some register
> (not sure about Kirkwood). It looks like that there is at least revision
> Z0 and revision A0 of some Kirkwood SoC.
>
> If there is a bug in first revisions then it should be documented in
> some Kirkwood Errata document. Unfortunately I have never seen it, it is
> not public, so I have no idea. In any case, if somebody has access to
> Marvell documents, interesting are these document numbers:
>
> * MV-S105223-001 - Differences Between the 88F6192, and 88F6281 Stepping Z0 and A0
> * MV-S501081-00 - 88F6180, 88F6192, and 88F6281 Functional Errata, Interface Guidelines, and Restrictions
> * MV-S501157-U0 - 88F6180, 88F6190, 88F6192, and 88F6281 Functional Errata, Interface Guidelines, and Restrictions
>
> One of the option how to investigate or debug this issue without
> documentation is to dump both BootROM versions (1.1, 1.2) and compare
> them. Either there is different UART protocol for booting (which needs
> to be implemented) or UART protocol is buggy and needs some workaround
> or it is completely broken and does not work.

Here is an excerpt from doc/develop/driver-model/serial-howto.rst.

Quote ===
Here are some things you might need to consider:

1. The serial driver itself needs to be present before relocation, so that the
   U-Boot banner appears. Make sure it has a u-boot,dm-pre-reloc tag
in the device
   tree, so that the serial driver is bound when U-Boot starts.

   For example, on iMX8::

       lpuart3: serial at 5a090000 {
           compatible = "fsl,imx8qm-lpuart";
           ...
       };

   put this in your xxx-u-boot.dtsi file::

       &lpuart3 {
           u-boot,dm-pre-proper;
       };
=== Unquote

So it looks like my understanding was correct. The serial driver is
not bound if there is no u-boot,dm-pre-reloc tag. And does it sound
like it is required for all targets because of this reason?

Thanks,
Tony