Add a files documenting what I've learned about the driver while working on various cleanups. Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> --- drivers/staging/media/atomisp/notes.txt | 30 +++++++++++++++++++++++++ 1 file changed, 30 insertions(+) create mode 100644 drivers/staging/media/atomisp/notes.txt diff --git a/drivers/staging/media/atomisp/notes.txt b/drivers/staging/media/atomisp/notes.txt new file mode 100644 index 000000000000..d128b792e05f --- /dev/null +++ b/drivers/staging/media/atomisp/notes.txt @@ -0,0 +1,30 @@ +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). -- 2.36.0
