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This speeds up memcpy by copying a word at a time if source and destination are aligned in mod 4. That is, if n and m are a positive integer: 4n -> 4m: aligned, 4x speed. 4n -> 4m+1: misaligned. 4n+1 -> 4m+1: aligned in mod 4, 4x speed. Ran the unit test on Peppy: > runtest ... Running test_memcpy... (speed gain: 120300 -> 38103 us) OK ... Ran make buildall -j: ... Running test_memcpy... (speed gain: 2084 -> 549 us) OK ... Note misaligned case is also optimized. Unit test runs in 298 us on Peppy while it takes about 475 with the original memcpy. TEST=Described above. BUG=chrome-os-partner:23720 BRANCH=none Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org> Change-Id: Ic12260451c5efd0896d6353017cd45d29cb672db Tested-by: Daisuke Nojiri <dnojiri@google.com> Reviewed-on: https://chromium-review.googlesource.com/185618 Reviewed-by: Randall Spangler <rspangler@chromium.org> Reviewed-by: Vincent Palatin <vpalatin@chromium.org> Commit-Queue: Daisuke Nojiri <dnojiri@google.com>
In the most general case, the flash layout looks something like this: +---------------------+ | Reserved for EC use | +---------------------+ +---------------------+ | Vblock B | +---------------------+ | RW firmware B | +---------------------+ +---------------------+ | Vblock A | +---------------------+ | RW firmware A | +---------------------+ +---------------------+ | FMAP | +---------------------+ | Public root key | +---------------------+ | Read-only firmware | +---------------------+ BIOS firmware (and kernel) put the vblock info at the start of each image where it's easy to find. The Blizzard EC expects the firmware vector table to come first, so we have to put the vblock at the end. This means we have to know where to look for it, but that's built into the FMAP and the RO firmware anyway, so that's not an issue. The RO firmware doesn't need a vblock of course, but it does need some reserved space for vboot-related things. Using SHA256/RSA4096, the vblock is 2468 bytes (0x9a4), while the public root key is 1064 bytes (0x428) and the current FMAP is 644 bytes (0x284). If we reserve 4K at the top of each FW image, that should give us plenty of room for vboot-related stuff.