GSoC 2014 [cbfs_media] Updates

This past week went into looking at the internal working of the cbfs_media interface. Some of the major observations were:

Locations of map() and read() calls
No read() calls at all. Also for the map() calls that were made, there weren’t any unmap() calls.

Size of mappings
The entire cbfs is pulled into the iram. There is a map call which puts about 28KB into the sram, to load romstage. The a10 has an sram of 32KB, hence we are using up most of the necessary ram.
The sequence followed is open() -> map()’s -> close().

Total Resources
Is just the sum of all the mappings, since there are no unmaps to subtract. This gives a benchmark to work upon. Now resource utilization is calculated each time coreboot loads, automatically and progress can tracked.
Now we are giving some thoughts on how to reduce the size of the mappings, one possibility being defining a limit (bound) on its size. What is happening currently, is the size is determined dynamically and hence some mappings are quite large. If we define a bound on it, and then repeat call ‘smaller’ map()s instead of one big one, that could do the job. But this wont always work as the decompression algorithm (LZMA) expects memory-mapped access to the entire compressed buffer. By the end of this week, we hope to strike a workaround this and get a more resource-efficient cbfs interface.

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