[U-Boot] Dynamically determine RAM size and pass it to kernel

[Michal Simek]

On 17.11.2016 15:09, Mike Looijmans wrote:
> On 17-11-16 13:34, Mike Looijmans wrote:
>> We have some Zynq based boards still in the field that have only 512MB
>> RAM
>> instead of 1GB. The memory chips are compatible and use the same settings
>> apart from that one extra address bit.
>>
>> So what works is just configure the DDR controller for 1GB and then
>> check if
>> writing some data "wraps" back, this is my "spike" code in the RAM
>> init code
>> for that:
>>
>> +       u32 *ptr_1 = (u32*)0x10000;
>> +       u32 *ptr_2 = (u32*)((gd->ram_size >> 1) + 0x10000);
>> +
>> +       puts("RAM test");
>> +       *ptr_1 = 0x12345678;
>> +       if (*ptr_2 == *ptr_1) {
>> +               *ptr_1 = 0x87654321;
>> +               if (*ptr_2 == *ptr_1) {
>> +                       puts(" [HALF]");
>> +                       gd->ram_size >>= 1;
>> +               }
>> +       }
> 
> I found that I can replace that with "get_mem_size()" which does this
> better.

You have some ways.
1. Rewrite dram_init() function to run this test.
2. Let SPL find out and add two dtbs to it.
   IIRC board_fit_config_name_match() is that function which can
   decide that.
3. If you use module, look at spd eeprom and read it which is something
   what I was playing with on zcu102. Freescale boards in past used
   this a lot.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Xilinx Microblaze
Maintainer of Linux kernel - Xilinx Zynq ARM and ZynqMP ARM64 SoCs
U-Boot custodian - Xilinx Microblaze/Zynq/ZynqMP SoCs


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