chromeec: support reading long battery strings

The Chrome EC currently supports two ways to read battery strings on
ACPI platforms:

 * Read up to 8 bytes from EC shared memory BMFG, BMOD, ...
 * Send a EC_CMD_BATTERY_GET_STATIC host command and read strings from
   the response. This is assumed to be exclusively controlled by the OS,
   because host commands' use of buffers is prone to race conditions.

To support readout of longer strings via ACPI mechanisms, this change
adds support for EC_ACPI_MEM_STRINGS_FIFO (https://crrev.com/c/5581473)
and allows ACPI firmware to read strings of arbitrary length (currently
limited to 64 characters in the implementation) from the EC and to
determine whether this function is supported by the EC (falling back to
shared memory if not).

BUG=b:339171261
TEST=on yaviks, the EC console logs FIFO readout messages when used in
     ACPI and correct strings are shown in the OS. If EC support is
     removed, correct strings are still shown in the OS.
BRANCH=nissa

Change-Id: Ia29cacb7d86402490f9ac458f0be50e3f2192b04
Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82775
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>

0 files changed, 0 insertions, 0 deletions