The way to do this without 'aticonfig' is to add "amdgpu.direct_gma_size=X" as a kernel boot parameter, where X is the size in MB to be allocated for DirectGMA/bus addressable memory (the maximum is typically 96MB). To verify this worked after adding the kernel parameter and rebooting is to run:
$ dmesg | grep -i gma
and then check clinfo for the "cl_amd_bus_addressable_memory" flag. I found the more detailed steps here: https://github.com/yadav26/radeonDGMA
I verified this on my setup:
OS: AlmaLinux 8.9
kernel: 4.18.0-240.el8.x86_64
amdgpu driver: amdgpu-pro-21.10-1263777-rhel-8.3
GPU: FirePro W5100
$ dmesg | grep -i gma
[ 4.086729] [drm] 96MB VRAM/GTT reserved for Direct GMA
$ clinfo | grep -i bus_add
Extensions: cl_khr_fp64 cl_amd_fp64 cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_3d_image_writes cl_khr_byte_addressable_store cl_khr_gl_sharing cl_amd_device_attribute_query cl_amd_vec3 cl_amd_printf cl_amd_media_ops cl_amd_media_ops2 cl_amd_popcnt cl_khr_image2d_from_buffer cl_amd_bus_addressable_memory cl_khr_spir cl_khr_gl_event
