[U-Boot] DDR training code for Armada 38x

[Chris Packham]

For the internet historians,

On Thu, Sep 21, 2017 at 4:25 PM, Chris Packham <judge.packham at gmail.com> wrote:
> On Wed, Sep 20, 2017 at 5:31 PM, Stefan Roese <sr at denx.de> wrote:
>> Hi Chris,
>>
>> On 19.09.2017 20:58, Chris Packham wrote:
>>>
>>> When you did the port from Marvell's source did you script any of the
>>> tidy-up that you did along the way?
>>
>>
>> Not really. At least not in a reproducible way. I spent long
>> hours running Lindent, recursive-replace tools and especially
>> manual code inspection and re-formatting on this huge code.
>> Still the outcome is far from perfect, but hopefully better
>> that the original version.
>>
>>> I'm running up a new board and with the upstream u-boot DDR training
>>> occasionally fails. But with the Marvell bootloader it doesn't fail.
>>> The initial port was done from TIP-1.29 but Marvell are now up to
>>> TIP-1.55 so there is probably some difference that results in my board
>>> working.
>>>
>>> One difference I've spotted so far is that Marvell enable 2T timing
>>> mode for all Armada 38x boards (the comment says "resolve low freq
>>> instability"). But doing that doesn't magically make my board work.
>>
>>
>> Did you compare all DDR register values (the "good" ones and the "bad"
>> ones) and only the the 2T timing is different?
>>
>
> There are more differences. 2T was the one that stuckout. As you know
> working backwards from register values to where the code sets them can
> be tricky with this code.
>
>>> I'm thinking I need to compare TIP-1.29 with TIP-1.55 to look for
>>> other differences but obviously that's going to be hard given the
>>> style changes.
>>
>>
>> Has the style changed in between the Marvell versions as well? I
>> have not looked into this code for quite some time.
>>
>
> What I meant was u-boot has 1.29 and I have 1.55 from Marvell. The
> oldest Marvell version I have is 1.34 which helped me find the 2T
> thing. I'm wondering what differences exist between 1.29 and 1.34.
> 1.55 also has support for some newer integrated switch+CPU chips so it
> is a little hard to separate those bits from the A38X code.
>
>>> If you have any scripts (or even just a record of the
>>> regexes) that you used would you be able to share them?
>>
>>
>> Please find some scripts attached, I've located that I have used while
>> doing this porting.
>
> Thanks. That's a start at least.

In the end once I fixed the ecc_scrubbing[1] I stopped seeing the
training failures so I've basically stopped looking at the differences
between the Marvell bootloader and u-boot. But in the meantime I can
summarize the differences I have identified in case they might help
someone in the future.

* Marvell unconditionally enable 2T timing for A38X
* Different settings for RD/WR ODT particularly in situations using
only one chip-select.

There are more differences in the register dumps but I haven't looked
into the meaning of them.

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[1] - https://lists.denx.de/pipermail/u-boot/2017-September/307243.html