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

[Tony Dinh]

Hi Stefan,

On Fri, Feb 3, 2023 at 4:11 PM Tony Dinh <mibodhi at gmail.com> wrote:
>
> Hi Pali,
>
> On Fri, Feb 3, 2023 at 2:05 PM Pali Rohár <pali at kernel.org> wrote:
> >
> > On Thursday 02 February 2023 19:04:45 Pali Rohár 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.
> >
> > BootROM is mapped to 0xF8000000 address and is 64 kB long. So via U-Boot
> > md command it is possible to dump it over console. Or via ext4write
> > command store it so ext4 fs on sd card / sata disk.
>
> Thanks for the info. It will be a while before I can get back to this
> BootROM 1.1 vs 1.2 topic.
>

I  have run some more tests, and am quite positive that if the uart0
node exists in the DTS, it must be tagged with dm,pre-reloc. That is
consistent with the serial documentation in
doc/develop/driver-model/serial-howto.rst. The issue is whether the
uart0 node is specified in the DTS. If it is, the dm-pre-reloc tag
must also be used.

To prove my theory, I've modified the Pogo V4 DTS to look exactly like
the NSA310S, as far as uart0 is concerned. The NSA310S does not even
have a uart0 node! and DM_SERIAL boots fine with this box. With the
patch below, the Pogo V4 can be kwboot and run normally. No
dm-pre-reloc tag is needed.

diff --git a/arch/arm/dts/kirkwood-pogoplug-series-4.dts
b/arch/arm/dts/kirkwood-pogoplug-series-4.dts
index 5aa4669ae2..227d5ff802 100644
--- a/arch/arm/dts/kirkwood-pogoplug-series-4.dts
+++ b/arch/arm/dts/kirkwood-pogoplug-series-4.dts
@@ -24,7 +24,8 @@
        };

        chosen {
-               stdout-path = "uart0:115200n8";
+               bootargs = "console=ttyS0,115200";
+               stdout-path = &uart0;
        };

        gpio_keys {
@@ -97,10 +98,6 @@
        };
 };

-&uart0 {
-       status = "okay";
-};
-
 /*
  * This PCIE controller has a USB 3.0 XHCI controller at 1,0
  */

Also, note that just enabling DEBUG_UART would always make the board
frozen when u-boot starts. So this was another factor why it took me
so long to figure this out :) I've just restored everything and
removed the uart0 node from the Pogo V4 DTS like above and it is
working.

But of course, we don't want to change the Pogo V4 DTS, so I will
submit another patch just for the Pogo V4 to add -u-boot.dtsi for this
box to enable the dm-pre-reloc tag for uart0.

Thanks,
Tony