Convert vboot hash calculation from task to deferred function

Vboot hash calculation takes ~350 ms during EC boot.  Since the hash
task is higher priority than the hook task, this starves all the hooks
during boot.

We could, in theory, fix that simply by swapping the priority of the
hook and hash tasks.  But then watchdog detection (in the hook task)
wouldn't detect hangs in the hash task.

A better fix (implemented here) is to convert the hashing operation to
a series of deferred function calls.  This gets rid of the hash task
entirely, and allows all pending hooks and other deferred function
calls to take place between each chunk of hashing.

On STM32-based boards, we need to bump up the hook task stack size,
since hashing is called from several layers deep in the hook task
instead of at the top of its own task, but this is still a net win of
several hundred bytes of SRAM.

BUG=chrome-os-partner:24892
BRANCH=rambi
TEST=Boot EC; look for "hash start" and "hash done" debug output.
     'taskinfo' shows at least 32 bytes of unused stack for HOOKS task.
     'hash ro' runs properly from EC console.

Change-Id: I9e580dc10fc0bc8e44896d84451218ef67578bbe
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/181954

1 files changed, 3 insertions, 0 deletions

diff --git a/chip/stm32/config_chip.h b/chip/stm32/config_chip.h
index 2d439a800e..afc2afe32c 100644
--- a/chip/stm32/config_chip.h
+++ b/chip/stm32/config_chip.h
@@ -36,6 +36,9 @@
 /* Default task stack size */
 #define TASK_STACK_SIZE 488
 
+/* Larger task stack size, for hook task */
+#define LARGER_TASK_STACK_SIZE 640
+
 /* Interval between HOOK_TICK notifications */
 #define HOOK_TICK_INTERVAL (500 * MSEC)