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

[Tony Dinh]

Added Simon to the discussion.

On Wed, Feb 1, 2023 at 1:13 PM Tony Dinh <mibodhi at gmail.com> 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.
>
> When I test new u-boot images for boards such as Dockstar or iConnect,
> I run kwboot with the GoFlex Home/Net. And they boot fine to a point
> that allows me to see that the image is good enough. So in the
> development phase, most if not all Kirkwood u-boot images can be
> booted over UART. Some with real boards, some with surrogates.
>
> > > 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.
>
> When u-boot,dm-pre-reloc is not specified in the uart0 DTS node, after
> the image was transferred by kwboot, the serial console is silent and
> the board is frozen.
>
> If I understand correctly, it is because before u-boot relocation, if
> DM serial is enabled, the serial uclass is present, but it has not
> been initialized (I think it is created but not "bind(?)" ). The
> dm-preloc property works because it explicitly tells DM to fully
> initialize the uclass before relocation. That was just my observation
> about DM in general, devices do not get fully initialized until the
> first use. So I tried the u-boot,dm-pre-reloc and it works. If my
> assumption is incorrect, perhaps somebody can look at the serial
> uclass and see if there is a different type of issue there.
>
> Thanks,
> Tony
>
> > >
> > > > > >
> > > > > > 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
> > >