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authorVadim Bendebury <vbendeb@chromium.org>2011-09-29 17:27:15 -0700
committerStefan Reinauer <stefan.reinauer@coreboot.org>2012-03-29 20:14:25 +0200
commit32da8bed197c5c7efc226dd9cfc3b75bad496f05 (patch)
tree054390e68ca9f95ef166dc3965de8d247e783271 /documentation
parentc34b4631282e03aba5b2c4b247ecc9a783924d0f (diff)
downloadcoreboot-32da8bed197c5c7efc226dd9cfc3b75bad496f05.tar.xz
CBMEM CONSOLE: Add CBMEM console driver implementation.
The CBMEM console driver saves console output in a CBMEM area, which then is made available to Linux applications for perusing. There are some system limitations which need to be worked around to achieve this goal: - some console traffic is generated before DRAM is initialized, leave alone CBMEM initialized. - after the RAM based stage starts, a lot of traffic is generated before CBMEM is initialized. As a result, the console log lives in three different places - the bottom of the cache as RAM space, the CBMEM buffer (where it is expected to be) and a static buffer used early in the RAM stage. When execution starts (in the cache as RAM mode), the console buffer is allocated at the bottom of the cache as RAM memory address range. Once DRAM is initialized, the CBMEM structure is initialized, and then the console buffer contents are copied from the bottom of the cache as RAM space into the CBMEM area right before the cache as RAM mode is disabled. The src/lib/cbmem_console.c:cbmemc_reinit() takes care of the copying. At this point the cache as RAM memory is about to be disabled, but the ROM stage is still going generating console output. To make sure this output is not lost, cbmemc_reinit() saves the new buffer address at a fixed location (0x600 was chosen for this), and the actual "printing" function checks to see if the RAM is already initialized (the stack is in RAM), and if so, gets the console buffer pointer from this location instead of using the cache as RAM address. When the RAM stage starts, a static buffer is used to store the console output, as the CBMEM buffer location is not known. Then, when CBMEM is reinitialized, cbmemc_reinit() again takes care of the copying. In case the allocated buffers are not large enough, the excessive data is dropped, and the copying routine adds some text to the output buffer to indicate that there has been data lost and how many characters were dropped. Change-Id: I8c126e31db6cb2141f7f4f97c5047f39a8db44fc Signed-off-by: Vadim Bendebury <vbendeb@chromium.org> Reviewed-on: http://review.coreboot.org/719 Tested-by: build bot (Jenkins) Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
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