LS1088A DDR Size

[cuongkelvin]

Hello,

we are having a DDR4 size problem on LS1088a platform.  We have 4GB DDR4 on the board. When u-boot starts it is confirmed that board has 4GB DDR4. But when we checked on kernel with free commands, it shows that RAM is 2GB.  I was delete the "mcmemsize" variable from my U-Boot configuration. Do you have any idea why are we having mismatch DDR size in u-boot and kernel ?

Attached photos you can see the differences.

[cuongkelvin]

Thank for reply.
If I delete "mcmemsize" will network performance decrease?

[yipingwang]

Yes, it will.

[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