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With this, we are able to boot with a super dead battery even with a bad charger. This however breaks support for chargers that cannot even supply 100mA, but that's very unlikely to happen. BUG=chrome-os-partner:21107 TEST=Charge a dead battery with a bad charger and a super long cable. BRANCH=Spring Change-Id: I3c532523456185223420a4381f56365ad3afb2ec Original-Change-Id: I6b7b0df0ae7bdf863420755ea92e09d87f6866c3 Signed-off-by: Vic Yang <victoryang@chromium.org> Reviewed-on: https://gerrit.chromium.org/gerrit/63804 Reviewed-by: Vincent Palatin <vpalatin@chromium.org> Reviewed-on: https://gerrit.chromium.org/gerrit/64276
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.