Zynq MPSoC Dynamic DDR DIMM Configuration support

[Michal Simek <michal.simek@xilinx.com>]

Hi,

On 5/13/21 9:24 AM, Jorge Ramirez-Ortiz, Foundries wrote:
> On 13/05/21, Michal Simek wrote:
>> Hi Jorge,
>>
>> On 5/12/21 11:21 PM, Jorge Ramirez-Ortiz, Foundries wrote:
>>> Hi Michal
>>>
>>> We are doing some work on an MPSoC UZ3EG platform part of which
>>> requires us to replace FSBL with SPL.
>>
>> Just for curiosity what's the reason for this requirement that fsbl is
>> not enough?
> 
> we prefer to have a common boot strategy on all the boards we support
> (whether it is from NXP, Xilinx, ST or TI); it just simplifies the OTA
> process (including their firmwares); and of course our meta layers.
> 
>>
>>>
>>> It seems the actual boot process is becoming an issue on these SoCs;
>>> currently, 1) we embed the PMU firmware on SPL so the bootrom can
>>> extract it and program it;
>>
>> Actually it is not working like this. PMU FW is own part of boot.bin and
>> it is not embed in SPL.
> 
> yes, absolutely (boot.bin is what we have been flashing), holding SPL and FW 
> 
>>
>>
>>> 2) then SPL configures the PMU using a
>>> platform specific binary that gets built also with SPL; 
>>
>> PMU cfg object.
> 
> yep, pm_cfg_obj.c
> 
>>
>>
>> and finally,
>>> 3) SPL sets up the DDR using its psu_init_gpl.c settings (also board
>>> specific, part of the XSA).
>>
>> yes.
>>
>>>
>>> It is this final step in the boot sequence that is being broken by the
>>> Dynamic DDR DIMM configuration feature [1]
>>>
>>> [1] https://www.xilinx.com/support/answers/75768.html
>>
>> This was developed for zcu102 and maybe others boards which have DIMM
>> modules where origin part were EOL.
> 
> right.
> 
> but notice that there is also support on u-boot for
> altera/imx/marvell/microchip; so just wondering if we should add
> drivers/ddr/xilinx to this list.  

Also SPD code is around too.



>>
>>
>>> Are you aware of any work in progress to support this? Any thoughts on
>>> how to work around it and train the DDR? will the functionality
>>> required to implmenet Dynamic DDR DIMM configuration be added as a
>>> separate file to the XSA tarball or will we need to do some native
>>> implementation in SPL?
>>
>> I am not aware about any work on SPL side to support this. IIRC FSBL
>> didn't have generic DDR configuration. It was only by reading SPD and
>> aligned some parameters but it is quite a long time I have looked at it
>> last time.
> 
> ok
> 
>>
>>
>>> Becase without a change in the last link in the process chain
>>> described earlier (calls to psu_init()), DDR just wont be accessible
>>> to U-BOOT or OP-TEE.
>>>
>>> In our case, we were able to boot from QSPI, boot SPL (in OCM), have
>>> SPL unpack and validate the FIT image, execute TF-A(in OCM), but then
>>> any jumps to OP-TEE or U-BOOT would obviously not progress since the
>>> DDR wasnt properly trained/initialized.
>>>
>>> so, any thoughts or plans you can share?
>>
>> The question is why you need this feature to be there. It is not working
>> for every DIMM module. And normally if you have custom boards you need
>> just one DDR configuration (or limited number based on HW versions) and
>> for that there is really no need to waste your boot up time on it.
> 
> not sure what you mean. we need this feature because it adds the
> expected flexibility to the bootloader. Sure, we can hardcode DDR
> configurations but why should we when it can be resolved by
> software. Am I missing your point?

Ok. One is support for evaluation boards and the second for a product.
In product you don't need this because I would say most of projects are
not using DIMMs.
If you want to support generic evaluations boards then of course it can
be done.

> 
>> You can add multiple configurations to psu_init_gpl() and based on any
>> information (board rev/pins/etc) decided which one should be used.
> 
> so what you are suggesting is that we customize psu_init_gpl() to the
> target (ie, have an updated xsa file with whatever config we need for
> this system).  

In products yes.

> 
> what I fail to grasp is why we can't take a step forward and do what
> we do for other architectures in u-boot. and what fsbl already does by
> config.
> 
> I mean, why not? do you foresee any integration issues with the
> current bootflow?

Not really if you are willing to write that code just go for it.
I think it is definitely feasible to do so but I haven't seen any
algorithm to do it in generic way even there must be one behind in
xilinx tools. There are a lot of types of memories which you can
configure in xilinx design tools but it won't be any problem to limit it
to some.

Thanks,
Michal