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

[Igor Grinberg]

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.

-- 
Regards,
Igor.