stm32l: Add a "PRE_FREQ_CHANGE" hook to allow other code to prepare

Before this change drivers had no way of knowing that a frequency
change was coming.  This could cause problems for some drivers (like
i2c) that need to make sure that a transaction isn't happening while a
frequency change is happening.

The PRE_FREQ_CHANGE archiecture is very simple here and we don't allow
any way to cancel it.

At the moment, we guarantee:
- We won't call PRE_FREQ_CHANGE with interrupts disabled, so acquiring
  locks / sleeping is OK.
- We'll call the actual HOOK_FREQ_CHANGE after the PRE_FREQ_CHANGE.

PRE_FREQ_CHANGE and HOOK_FREQ_CHANGE should not use deferred function
calls.

BRANCH=pit
BUG=chrome-os-partner:22093
TEST=With all patches together:
- on AP: suspend_stress_test
- on EC: battery 10000 50

Change-Id: I2731a3e85d41e749fa571fdb74b5c9b12043cda6
Signed-off-by: Doug Anderson <dianders@chromium.org>
Previous-Reviewed-on: https://chromium-review.googlesource.com/167101
(cherry picked from commit d84c0dbbf7c5a72917a820e292ecfdfa698d0fb9)
Reviewed-on: https://chromium-review.googlesource.com/167148
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/link_defs.h b/include/link_defs.h
index a9c9e97e41..d5e4ccd595 100644
--- a/include/link_defs.h
+++ b/include/link_defs.h
@@ -20,6 +20,8 @@ extern const struct console_command __cmds_end[];
 /* Hooks */
 extern const struct hook_data __hooks_init[];
 extern const struct hook_data __hooks_init_end[];
+extern const struct hook_data __hooks_pre_freq_change[];
+extern const struct hook_data __hooks_pre_freq_change_end[];
 extern const struct hook_data __hooks_freq_change[];
 extern const struct hook_data __hooks_freq_change_end[];
 extern const struct hook_data __hooks_sysjump[];