cbfs: Add LZ4 in-place decompression support for pre-RAM stages

This patch ports the LZ4 decompression code that debuted in libpayload
last year to coreboot for use in CBFS stages (upgrading the base
algorithm to LZ4's dev branch to access the new in-place decompression
checks). This is especially useful for pre-RAM stages in constrained
SRAM-based systems, which previously could not be compressed due to
the size requirements of the LZMA scratchpad and bounce buffer. The
LZ4 algorithm offers a very lean decompressor function and in-place
decompression support to achieve roughly the same boot speed gains
(trading compression ratio for decompression time) with nearly no
memory overhead.

For now we only activate it for the stages that had previously not been
compressed at all on non-XIP (read: non-x86) boards. In the future we
may also consider replacing LZMA completely for certain boards, since
which algorithm wins out on boot speed depends on board-specific
parameters (architecture, processor speed, SPI transfer rate, etc.).

BRANCH=None
BUG=None
TEST=Built and booted Oak, Jerry, Nyan and Falco. Measured boot time on
Oak to be about ~20ms faster (cutting load times for affected stages
almost in half).

Change-Id: Iec256c0e6d585d1b69985461939884a54e3ab900
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/13638
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

2 files changed, 6 insertions, 2 deletions

diff --git a/payloads/libpayload/include/cbfs_core.h b/payloads/libpayload/include/cbfs_core.h
index 4c59f4131a..4cbc4c0628 100644
--- a/payloads/libpayload/include/cbfs_core.h
+++ b/payloads/libpayload/include/cbfs_core.h
@@ -58,6 +58,7 @@
 
 #define CBFS_COMPRESS_NONE  0
 #define CBFS_COMPRESS_LZMA  1
+#define CBFS_COMPRESS_LZ4   2
 
 /** These are standard component types for well known
     components (i.e - those that coreboot needs to consume.
diff --git a/payloads/libpayload/include/lz4.h b/payloads/libpayload/include/lz4.h
index 1f2830db46..d2120a48fc 100644
--- a/payloads/libpayload/include/lz4.h
+++ b/payloads/libpayload/include/lz4.h
@@ -36,7 +36,10 @@
 
 /* Decompresses an LZ4F image (multiple LZ4 blocks with frame header) from src
  * to dst, ensuring that it doesn't read more than srcn bytes and doesn't write
- * more than dstn. Buffer sizes must stay below 2GB.
+ * more than dstn. Buffer sizes must stay below 2GB. Can decompress files loaded
+ * to the end of a buffer in-place, as long as buffer is larger than the final
+ * output size. (Usually just a few bytes, but may be up to (8 + dstn/255) in
+ * worst case. Will reliably return an error if buffer was too small.)
  * Returns amount of decompressed bytes, or 0 on error.
  */
 size_t ulz4fn(const void *src, size_t srcn, void *dst, size_t dstn);
@@ -44,4 +47,4 @@ size_t ulz4fn(const void *src, size_t srcn, void *dst, size_t dstn);
 /* Same as ulz4fn() but does not perform any bounds checks. */
 size_t ulz4f(const void *src, void *dst);
 
-#endif /* __LZO_H_ */
+#endif /* __LZ4_H_ */