Mapping ram memory using ioremap

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.