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>

6 files changed, 21 insertions, 2 deletions

diff --git a/chip/stm32/clock-stm32l.c b/chip/stm32/clock-stm32l.c
index 4d5b1babeb..e89c2e3ef5 100644
--- a/chip/stm32/clock-stm32l.c
+++ b/chip/stm32/clock-stm32l.c
@@ -59,6 +59,9 @@ static void clock_set_osc(enum clock_osc osc)
 	if (osc == current_osc)
 		return;
 
+	if (current_osc != OSC_INIT)
+		hook_notify(HOOK_PRE_FREQ_CHANGE);
+
 	switch (osc) {
 	case OSC_HSI:
 		/* Ensure that HSI is ON */
diff --git a/common/hooks.c b/common/hooks.c
index cd2941434c..59038008a8 100644
--- a/common/hooks.c
+++ b/common/hooks.c
@@ -33,6 +33,7 @@ struct hook_ptrs {
  */
 static const struct hook_ptrs hook_list[] = {
 	{__hooks_init, __hooks_init_end},
+	{__hooks_pre_freq_change, __hooks_pre_freq_change_end},
 	{__hooks_freq_change, __hooks_freq_change_end},
 	{__hooks_sysjump, __hooks_sysjump_end},
 	{__hooks_chipset_pre_init, __hooks_chipset_pre_init_end},
diff --git a/core/cortex-m/ec.lds.S b/core/cortex-m/ec.lds.S
index c5d90265ce..115310bc28 100644
--- a/core/cortex-m/ec.lds.S
+++ b/core/cortex-m/ec.lds.S
@@ -60,6 +60,10 @@ SECTIONS
         *(.rodata.HOOK_INIT)
         __hooks_init_end = .;
 
+        __hooks_pre_freq_change = .;
+        *(.rodata.HOOK_PRE_FREQ_CHANGE)
+        __hooks_pre_freq_change_end = .;
+
         __hooks_freq_change = .;
         *(.rodata.HOOK_FREQ_CHANGE)
         __hooks_freq_change_end = .;
diff --git a/core/host/host_exe.lds b/core/host/host_exe.lds
index 04e605287b..15925213a7 100644
--- a/core/host/host_exe.lds
+++ b/core/host/host_exe.lds
@@ -24,6 +24,10 @@ SECTIONS {
     *(.rodata.HOOK_INIT)
     __hooks_init_end = .;
 
+    __hooks_pre_freq_change = .;
+    *(.rodata.HOOK_PRE_FREQ_CHANGE)
+    __hooks_pre_freq_change_end = .;
+
     __hooks_freq_change = .;
     *(.rodata.HOOK_FREQ_CHANGE)
     __hooks_freq_change_end = .;
diff --git a/include/hooks.h b/include/hooks.h
index 2ef5523d1d..6862005379 100644
--- a/include/hooks.h
+++ b/include/hooks.h
@@ -46,9 +46,14 @@ enum hook_type {
 	/*
 	 * System clock changed frequency.
 	 *
-	 * Hook routines are called from the context which initiates the
-	 * frequency change.
+	 * The "pre" frequency hook is called before we change the frequency.
+	 * There is no way to cancel.  Hook routines are always called from
+	 * a task, so it's OK to lock a mutex here.  However, they may be called
+	 * from a deferred task on some platforms so callbacks must make sure
+	 * not to do anything that would require some other deferred task to
+	 * run.
 	 */
+	HOOK_PRE_FREQ_CHANGE,
 	HOOK_FREQ_CHANGE,
 
 	/*
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[];