Linux/AM5728: CMEM and omap_bo differences

Hello,

omap_bo is a drm buffer which can directly go to display. Please check this guide for more information:
processors.wiki.ti.com/.../Linux_Core_DSS_User's_Guide

Hope this helps.

BR
Margarita

CMEM memory is contiguous memory having support for buffer caching operation by the CMEM driver. OMAP_BO is omapdrm buffer manager and typically allocates memory from TILED memory pool limited to 128 MB in size.

Typically CMEM pool is used for DSP memory need/openCL franework. It is also recommended to use CMEM pool for capture/display other IPs when the buffer is accessed by ARM also for software processing. Since OMAP_BO buffers aren't cached, the software processing on those buffers is very slow. When allocated through CMEM, the cached operations can be managed and the buffers can be exported to linux driver using DMABUF API protocol.

Refer to dual camera example application loopback.c file to see the CMEM buffer and OMAP_BO buffer allocation and usage.

In current implementation on AM57x, omapdrm allocates buffers (both dumb and omap_bo) from TILER 1D space, unless the user asks for TILER 2D buffer. TILER region is limited to 128 MB , restriction coming from HW by the DMM IP.

You can find the code for TILER memory management under drivers\gpu\drm\omapdrm folder. You can learn more about TILER memory in TRM. Please refer to chapter 15 on Memory Subsystem.