[U-Boot] [PATCH 0/3] Add generic FDT memory bank decoding and gd initialization

[Michal Simek]

On 12.12.2016 09:24, Igor Grinberg wrote:
> On 12/12/16 10:02, Michal Simek wrote:
>> On 12.12.2016 08:13, Nathan Rossi wrote:
>>> On 12 December 2016 at 03:11, Igor Grinberg <grinberg at compulab.co.il> wrote:
>>>> dropping the list for this one as the question seems to me irrelevant to your patch set.
>>>>
>>>> On 12/11/16 18:47, Nathan Rossi wrote:
>>>>> On 12 December 2016 at 01:08, Igor Grinberg <grinberg at compulab.co.il> wrote:
>>>>>> Hi Nathan,
>>>>>>
>>>>>> On 12/11/16 15:58, Nathan Rossi wrote:
>>>>>>> This series adds two functions for handling the memory bank decoding and
>>>>>>> initialization of global data for use by boards in their dram_init and
>>>>>>> dram_init_banksize functions.
>>>>>>
>>>>>> I might have missed some discussions on this meter,
>>>>>> can you please provide the use cases for this?
>>>>>> IMO, the bootloader's job is to initialize the DRAM, detect its size, and pass
>>>>>> the detected DRAM configuration on to an OS.
>>>>>
>>>>> Hi Igor,
>>>>>
>>>>> I do not think there have been any discussions on this (at least none
>>>>> that I am aware of).
>>>>>
>>>>> Some boards (like Zynq and ZynqMP ones) are using
>>>>> CONFIG_SYS_SDRAM_SIZE to define the amount of memory that is available
>>>>> (since detection is not possible).
>>>>
>>>> May I ask why is detection not possible on these boards (may be SoCs)?
>>>
>>> That is correct, Zynq and ZynqMP are ARM SoCs. Which in the majority
>>> of cases are used in boards which have fixed memory device setups
>>> (without any SPD or equivalent).
>>
>> For example zcu102 zynqmp development board is using modules with SPD on
>> it but if you look at generic SPD support then you will find out that
>> FSL(drivers/ddr/fsl) is one of the major platform which is using it for
>> ddr size detection.
>> Anyway as Nathan wrote above the majority of boards with zynq/zynqmp
>> devices need to be configured at build time or at run time by DTB.
>>
>> There is also topic.nl boards which contain ddr configuration the same
>> for different ddr sizes and Mike sent this patch to get it work
>> http://lists.denx.de/pipermail/u-boot/2016-November/273385.html
> 
> That's exactly my point. I think Mike's patch does a way better job
> detecting at run time than any compiled in or a DT based pseudo detection...
> 
>>
>> Anyway in general there are some ways how to configure DDR size
>> - build time setup (CONFIG_SYS_SDRAM*)
>> - run time setup
>> 	- ddr detection
>> 		- via SPD (like FSL)
>> 		- via algorithm (like topic.nl)
>> 	- configuration
>> 		- read DTB
>>
>> Nathan's path is trying to address last run time DTB configuration
>> method to be shared across platforms because similar stuff Uniphier is
>> using too. And it doesn't make sense to copy that functions everywhere
>> that's why this should go core parts.
> 
> Yep. That's exactly what I thought. I see Nathan's patch set as an
> improvement of the current situation anyway.
> 
> Also I think Mike's patch does a much better job on this.
> 

Just keep in your mind just in case that you know that your
configuration supports it. If you don't have DDR connected to hard block
and you use ddr to PL you don't even know where to look for DDR.
And with arm64 it is pretty huge space.
It means we really have to provide ways how to do it and these patches
are just generic way how to do it via reading DTB instead of code
duplication (+ bug) which we have now.

Thanks,
Michal