Mapping ram memory using ioremap

[noman pouigt]

We are using part of DRAM as shared memory
between DSP and SoC. However, DSP
can only access higher 1GB of DRAM.

In order to map the aforementioned memory
I tried using ioremap and it blurted out the
warning as mentioned in this article.
https://lwn.net/Articles/409700/

What is the alternative to using ioremap to
map specific RAM memory region for use
in the driver as shared memory?

I tried memremap + reserved memory as well
and it failed.