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Detect DDR size in u-boot on i.mx8m

Question asked by Richard Hu on Jun 6, 2018
Latest reply on Jun 27, 2018 by Richard Hu

Hello, Sir:


We have a model of custom i.mx8m board but it comes with different size of LPDDR4.(1GB, 2GB and 3GB)

And we have different resistors for GPIO to identify the size of LPDDR4 on boards.

In SPL, it detects the size of LPDDR4 and applies corresponding DDR initialization code generated by i.mx8m DDR tool.

It works fine.


The problem is in "dram_init" function in u-boot:

In this function, it has to assign the actual size of DRAM to "gd->ram_size" to inform u-boot of the available ddr size.

There are three possible approaches:

1. Utilize detection GPIO to identify DDR size: it doesn't work.

It seems that "dram_init" is in the very early stage. IOMUX doesn't even take effect.

I always get error code from "gpio_get_value". (The same code works in SPL.)


2. Utilize "get_ram_size" to get ddr size: it doesn't work for 3GB size.

There is constraint for "get_ram_size".

It only works for the size that is power of 2. So it doesn't work for 3GB.

It always returns 16 if i set the argument - "maxsize" as 3GB .


3. Get DDR size from memory controller:

It lacks of useful information of DDR controller in technical reference manual of i.mx8m.

Is there API like "imx_ddr_size" of i.mx6 for i.mx8m?

Or could you provide the information how i read DDR size from DDR controller?


Thanks you~!!!