| Some notes about the working of the atomisp drivers (learned while working |
| on cleaning it up). |
| |
| The atomisp seems to be a generic DSP(ISP) like processor without a fixed |
| pipeline. It does not have its own memory, but instead uses main memory. |
| The ISP has its own address-space and main memory needs to be mapped into |
| its address space through the ISP's MMU. |
| |
| Memory is allocated by the hmm code. hmm_alloc() returns an ISP virtual |
| address. The hmm code keeps a list of all allocations and when necessary |
| the hmm code finds the backing hmm-buffer-object (hmm_bo) by looking |
| up the hmm_bo based on the ISP virtual address. |
| |
| The actual processing pipeline is made by loading one or more programs, |
| called binaries. The shisp_240??0_v21.bin firmware file contains many |
| different binaries. Binaries are picked by filling a ia_css_binary_descr |
| struct with various input and output parameters and then calling |
| ia_css_binary_find(). Some binaries support creating multiple outputs |
| (preview + video frame?) at the same time. |
| |
| For example for the /dev/video0 preview node load_preview_binaries() |
| from atomisp/pci/sh_css.c is called and then loads a preview and |
| optionally a scalar binary. Note when digital zoom is disabled |
| (it is enabled by default) only the preview binary is loaded. |
| So in this case a single binary handles the entire pipeline. |
| |
| Since getting a picture requires multiple processing steps, |
| this means that unlike in fixed pipelines the soft pipelines |
| on the ISP can do multiple processing steps in a single pipeline |
| element (in a single binary). |
