[U-Boot] x86: Bay Trail support with W83627DHG

[Stefan Roese]

Hi Bin,

On 17.01.2016 03:35, Stefan Roese wrote:
> On 16.01.2016 15:08, Bin Meng wrote:
>> On Fri, Jan 15, 2016 at 10:37 PM, Stefan Roese <sr at denx.de> wrote:
>>> Hi Simon, Hi Bin!
>>>
>>> I'm currently busy with porting U-Boot to a Bay Trail board.
>>> Equipped with an Intel Atom E3845 and additionally the
>>> Nuvoton / Winbond W83627DHG Super IO chip.
>>>
>>> My staring point for this port is the Minnowboard MAX, which
>>> works very well btw. I've used the same binaries as described
>>> in the README.x86 as on the MinnowMAX for this new Bay Trail
>>> board. But am not able yet to see any output on the DEBUG_UART.
>>>
>>> Bin, you already mentioned in a previous mail, that I need to
>>> enable the legacy UART in the Super IO chip for this. I've
>>> started adding a small driver for this, similar to the one
>>> you've introduced for the SMSC:
>>
>> Ah, looks I delivered inaccurate information before! I just remember
>> BayTrail SoC integrates a legacy UART at I/O 0x3f8 and it is enabled
>> by FSP by default. If you use a debug version of FSP (only gold4
>> release provides a debug version FSP), you will se lots of useful
>> debug information printed on the serial port (the one connected to the
>> SoC legacy UART). But, why does your board have an additional Nuvoton
>> / Winbond W83627DHG Super IO chip? I guess it's for other legacy
>> peripherals like 8042 KBC, etc? We need figure out the serial port you
>> are trying to enable is connected to which chip. If it is connected
>> directly to BayTrail SoC, then you don't need program this W83627DHG.
>
> It is connected to the Winbond UART. So we need to enable and use it.
> But how can I disable the BayTrail internal legacy UART? So that the
> Winbond one is really used?

Okay. I was able to work around this problem with the included
legacy UART in the Bay Trail Atom. By moving the IO base address
of the Winbond COM1 from 0x3f8 to a different (unused) location.
And then using this new address as the UART base address. U-Boot
boots to the prompt with the "fixed" memory-down DDR parameters
to the FSP in this configuration.

Still I would really like to disable the internal legacy UART
and only use the Winbond UART(s) at the default address. Disabling
the Bay Trail legacy UART by clearing the "UART_CONT.COM1EN" bit,
as described in the "Intel AtomTM Processor E3800 Product Family
Datasheet", does not seem to fix this problem. I need to double
check this tomorrow though.

Bin, Simon, do you have any ideas on how to disable this Atom
legacy UART instead. It must be possible, as when booting into
Linux with the original BIOS, the Winbond COM1 works just fine
at 0x3f8.

Thanks,
Stefan