[U-Boot] Unable to boot evb-ast2500

[Cédric Le Goater]

On 08/06/2018 12:11 PM, Joel Stanley wrote:
> On Mon, 6 Aug 2018 at 19:39, Cédric Le Goater <clg at kaod.org> wrote:
>>
>> On 08/06/2018 05:25 AM, Joel Stanley wrote:
>>> Hello,
>>>
>>> I am attempting to boot evb-ast2500 in Qemu before flashing it to a
>>> system. It doesn't get past the DRAM step, due to getting stuck
>>> endlessly looping in some libfdt code.
>>>
>>> With some debugging turned on, I get this:
>>>
>>> OF: translating address: 0040781e
>>> OF: parent translation for: 00000000
>>> OF: one level translation: 0040781e
>>> OF: parent translation for: 00000000
>>> OF: one level translation: 0040781e
>>> OF: translating address: 00206e1e
>>>
>>>
>>> U-Boot 2018.09-rc1-00096-gbb694d4e898b-dirty (Aug 06 2018 - 12:27:22 +0930)
>>>
>>> Model: Aspeed BMC
>>> DRAM:  OF: translating address: 00006e1e
>>> OF: translating address: 00026e1e
>>> OF: translating address: 0050781e
>>> OF: parent translation for: 00000000
>>> OF: one level translation: 0050781e
>>> OF: parent translation for: 00000000
>>> OF: one level translation: 0050781e
>>> Watchdog timer expired.
>>>
>>> And then the watchdog causes the system to reboot. The build is master
>>> as of gbb694d4e898b, with the addition of some #define DEBUG.
>>>
>>> I don't think this is a qemu issue. If it is, I can work on fixing
>>> qemu, but I need some help on understanding what u-boot is doing.
>>
>> The sdram driver in U-Boot uses the watchdog1 and the SCU power
>> reset register to reset the SDRAM controller. Our QEMU emulation
>> is not precise enough I think.
> 
> Thanks for the pointer.
> 
> I was able to get u-boot to load to the prompt after some hacks to get
> rid of the watchdog requirement. It was a surprise to find out that
> the watchdog is used to reset the SDRAM controller!

The SDK also does but it uses wdt3 and only sets the enable reset SDRAM 
bit in the reset register mask. May be u-boot needs some improvements on
that part. 

> I have some patches to send to the qemu list that will allow it to run.

OK. we can add them to our QEMU branch

Thanks,

C.