The available capacity of the LX2160ARDB_REV2 DDR4 is 2 GB less than the actual physical capacity

[liushuangxin]

Hello nxp,

we use 2160 as CPU,LSDK 20.4,linux 5.4.3. We used 8 pieces of ddr particles with a capacity of 1GB. After entering the system, we used the free command to query only about 5.7G, which is more than 2 G less than the actual. We queried NXP's official lx2160ardb_rev2 demo board and found that the 32G physical memory display is only 29.7G.
I would like to ask if this kind of imagination exists in the SDK, or if there are other configurations that can be configured.

Thank you. Hope to get your reply!

[yipingwang · Accepted solution]

The lost DDR can be divided into 2 parts.
1) DDR used by NXP specific software, firmware components
2) DDR used by various segments of kernel.

For the first part,
1) u-boot uses memory till it is used, but once kernel boots, u-boot is swapped out of memory.
2) 66 MB is used by TF-A
3) MC can use anywhere between 512M to 2G (it depends on u-boot comandline argument 'mcmemsize'). The parameter mcmemsize defines amount of system DDR to be used by the Management Complex. If this variable is not defined, the compile-time value 0x70000000 or 1.75GB will be the default. Normally, users do not need to set this variable because the default is acceptable.

TF-A+MC is about 1.8G

kernel reserved=(18620K kernel code, 2476K rwdata, 8844K rodata, 5888K init, 993K bss, 406712K reserved, 327680K cma-reserved) = 771213K=0.7G

MemTotal in /proc/meminfo is 14232028 kB, the lost memory is about 16-13.6=2.4G(TF-A+MC+kernel reserved)

root@TinyLinux:~# cat /proc/meminfo
MemTotal: 14232028 kB
MemFree: 13596760 kB
MemAvailable: 13478276 kB

[liushuangxin]

Dear yiping，
Thank you for your reply, your answer is very helpful to me.
Best regrards