Dynamically determine RAM size and pass it to kernel
?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;
+ }
+ }
This works well, and reliably detects that the board only has half the amount of RAM, and corrects the ram_size variable.
The problem I'm seeing now is that this new ram_size does not get passed to the kernel. Apparently in modern versions of u-boot I need to somehow patch the "live" devicetree blob as well? How does that work?
Kind regards,
Mike Looijmans
System Expert
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Quoted 10 lines · Mike Looijmans
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:
(quoted diff) +2
-0+ u32 *ptr_1 = (u32*)0x10000; + u32 *ptr_2 = (u32*)((gd->ram_size >> 1) + 0x10000);
Review
Quoted 10 lines
(quoted diff) +10
-0+ + 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.
Quoted 7 lines
This works well, and reliably detects that the board only has half the amount of RAM, and corrects the
ram_sizevariable.The problem I'm seeing now is that this new
ram_sizedoes not get passed to the kernel. Apparently in modern versions of u-boot I need to somehow patch the "live" devicetree blob as well? How does that work?
Kind regards,
Mike Looijmans
System Expert
TOPIC Products
Materiaalweg 4, NL-5681 RJ Best Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijmans at topicproducts.com
Website: www.topicproducts.com
Please consider the environment before printing this e-mail
Quoted 25 lines · Mike Looijmans
Quoted 13 lines · Mike Looijmans
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:(quoted diff) +2
-0+ u32 *ptr_1 = (u32*)0x10000; + u32 *ptr_2 = (u32*)((gd->ram_size >> 1) + 0x10000);Review
Quoted 10 lines
(quoted diff) +10
-0+ + 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; + } + }
Quoted 2 lines
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
Signature · 14 lines
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 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 198 bytes Desc: OpenPGP digital signature URL: <http://lists.denx.de/pipermail/u-boot/attachments/20161118/16ab93d2/attachment.sig>