[PATCH 1/9] i2c: designware: Fix system suspend

[Ulf Hansson <ulf.hansson@linaro.org>]

The commit 8503ff166504 ("i2c: designware: Avoid unnecessary resuming
during system suspend"), may suggest to the PM core to try out the so
called direct_complete path for system sleep. In this path, the PM core
treats a runtime suspended device as it's already in a proper low power
state for system sleep, which makes it skip calling the system sleep
callbacks for the device, except for the ->prepare() and the ->complete()
callback.

Moreover, under certain circumstances the PM core may unset the
direct_complete flag for a parent device, in case its child device are
being system suspended before. In other words, the PM core doesn't skip
calling the system sleep callbacks, no matter if the device is runtime
suspended or not.

In cases of an i2c slave device, the above situation is triggered.
Unfortunate, this also breaks the assumption that the i2c device is always
runtime resumed, whenever the dw_i2c_plat_suspend() callback is being
invoked, which then leads to a regression.

More precisely, dw_i2c_plat_suspend() then calls clk_core_disable() and
clk_core_unprepare(), for an already disabled/unprepared clock, leading to
complaints about clocks calls being wrongly balanced.

In cases when the i2c device is attached to the ACPI PM domain, the problem
doesn't occur. That's because ACPI's ->suspend() callback, assigned to
acpi_subsys_suspend(), calls pm_runtime_resume() for the i2c device.

To make a simple fix for this regression, let's runtime resume the i2c
device in the ->prepare() callback, assigned to dw_i2c_plat_prepare(). This
prevents the direct_complete path from being executed by the PM core and
guarantees the dw_i2c_plat_suspend() is called with the i2c device always
being runtime resumed.

Of course this change is suboptimal, because to always force a runtime
resume of the i2c device in ->prepare() is a waste, especially in those
cases when it could have remained runtime suspended during the entire
system sleep sequence. However, to accomplish that behaviour a bigger
change is needed, so defer that to future changes not applicable as fixes
or for stable.

Fixes: 8503ff166504 ("i2c: designware: Avoid unnecessary resuming...")
Cc: stable@vger.linux.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/i2c/busses/i2c-designware-platdrv.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index d1263b8..2b7fa75 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -375,17 +375,11 @@ MODULE_DEVICE_TABLE(of, dw_i2c_of_match);
 #ifdef CONFIG_PM_SLEEP
 static int dw_i2c_plat_prepare(struct device *dev)
 {
-	return pm_runtime_suspended(dev);
-}
-
-static void dw_i2c_plat_complete(struct device *dev)
-{
-	if (dev->power.direct_complete)
-		pm_request_resume(dev);
+	pm_runtime_resume(dev);
+	return 0;
 }
 #else
 #define dw_i2c_plat_prepare	NULL
-#define dw_i2c_plat_complete	NULL
 #endif
 
 #ifdef CONFIG_PM
@@ -413,7 +407,6 @@ static int dw_i2c_plat_resume(struct device *dev)
 
 static const struct dev_pm_ops dw_i2c_dev_pm_ops = {
 	.prepare = dw_i2c_plat_prepare,
-	.complete = dw_i2c_plat_complete,
 	SET_SYSTEM_SLEEP_PM_OPS(dw_i2c_plat_suspend, dw_i2c_plat_resume)
 	SET_RUNTIME_PM_OPS(dw_i2c_plat_suspend, dw_i2c_plat_resume, NULL)
 };
-- 
2.7.4