On 03/22/2017 06:13 PM, Martin Michlmayr wrote:
Vagrant Cascadian observed that only 3.5 GB RAM are available on the
Jetson TX1 development kit.
[ 0.000000] Memory: 3501036K/3670016K available (6780K kernel code, 1020K rwdata, 2164K rodata, 3264K init, 634K bss, 168980K reserved, 0K cma-reserved)
Interestingly, even u-boot only shows 3.5 GB:
DRAM: 3.5 GiB
This is with mainline u-boot 2016.11 and R23.2 (2016.03-00633-g3ef9cdb).
That's expected.
A portion of the top-of-ram holds various carve-outs, such as for the
secure OS and perhaps other purposes like media buffers. Mainline U-Boot
currently hard-codes the size of this unusable RAM area to a very
conservative size. Ideally, U-Boot would query the size of the RAM from
the secure monitor, or retrieve it from information passed by an earlier
stage bootloader. However, doing so relies on using interfaces that may
not be strict ABIs, so we didn't want to make upstream U-Boot use them
at least when we first upstreamed T210 support.
However, 2015.07-rc2-g78c8468 (from R23.1.1) shows:
DRAM: 4 GiB
but that u-boot doesn't boot mainline kernels (some DT errors).
Conversely, the L4T version of U-Boot is expected to work with the
specific SW stack shipped with L4T, and hence does determine the
carveout size at runtime, and hence allows access to a bit more RAM.
L4T U-Boot should boot an upstream kernel without issue. You may need to
delete a few environment variables to stop U-Boot attempting to copy
some data from the NV-bootloader-supplied DTB into the DTB that U-Boot
itself loads from "disk" and passes to the kernel.
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