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

[Stefan Roese]

Hi Tony,

On 2/9/23 04:17, Tony Dinh wrote:
> 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
>    */

FWIU, you are hitting a bug in the early serial console code, perhaps
in serial_check_stdout()?

Could you please check if Pogo V4 boots with
CONFIG_REQUIRE_SERIAL_CONSOLE unset?

> Also, note that just enabling DEBUG_UART would always make the board
> frozen when u-boot starts.

This should not be the case of course. Are you sure you've correctly
configured the DEBUG UART?

> 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.

Understood.

Thanks,
Stefan