[PATCH v2 4/7] i2c: of-prober: Defer regulator_disable() on successful probe in simple helper

[Chen-Yu Tsai <wenst@chromium.org>]

When a I2C component is found, it's device node is immediately enabled.
This triggers device creation and driver binding. The prober will hold
the regulator enable reference across this part. If the driver probes
synchronously, then it happens within this window. On the other hand,
if the driver probes asynchronously, there is high chance that it
happens after the prober's cleanup function was called, in which case
the regulator would have been disabled when the driver's probe function
is called. This would then require the driver to wait 100 ms for the
hardware to reinitialize, even if the probe function was just a split
second late and the regulator was disabled a few milliseconds ago.

Recently, some of the drivers for the component that are targeted by the
I2C OF component prober gained the ability to skip waiting for hardware
initialization if the regulator was left enabled. This happens when the
PMIC has them on by default, or if the component prober left them on
after probing the component.

Wait a bit of time before dropping the enable refcount on our end so
that the actual driver has the opportunity to catch and increase the
refcount on their end. The 100 ms delay was arbitrarily chosen.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/i2c/i2c-core-of-prober.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-of-prober.c b/drivers/i2c/i2c-core-of-prober.c
index f274e260353c..17495125467e 100644
--- a/drivers/i2c/i2c-core-of-prober.c
+++ b/drivers/i2c/i2c-core-of-prober.c
@@ -243,11 +243,23 @@ static int i2c_of_probe_simple_enable_regulator(struct device *dev, struct i2c_o
 	return 0;
 }
 
-static void i2c_of_probe_simple_disable_regulator(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
+static void i2c_of_probe_simple_disable_regulator(struct device *dev,
+						  struct i2c_of_probe_simple_ctx *ctx,
+						  bool defer_disable)
 {
 	if (!ctx->supply)
 		return;
 
+	/*
+	 * Wait a bit of time for async drivers to probe and increase the
+	 * regulator enable count. This allows the drivers to check and
+	 * skip waiting for re-initialization.
+	 */
+	if (defer_disable) {
+		dev_dbg(dev, "Deferring regulator disable\n");
+		msleep(100);
+	}
+
 	dev_dbg(dev, "Disabling regulator supply \"%s\"\n", ctx->opts->supply_name);
 
 	regulator_disable(ctx->supply);
@@ -364,7 +376,7 @@ int i2c_of_probe_simple_enable(struct device *dev, struct device_node *bus_node,
 	return 0;
 
 out_disable_regulator:
-	i2c_of_probe_simple_disable_regulator(dev, ctx);
+	i2c_of_probe_simple_disable_regulator(dev, ctx, false);
 out_put_gpiod:
 	i2c_of_probe_simple_put_gpiod(ctx);
 out_put_supply:
@@ -409,7 +421,7 @@ void i2c_of_probe_simple_cleanup(struct device *dev, void *data)
 	i2c_of_probe_simple_disable_gpio(dev, ctx);
 	i2c_of_probe_simple_put_gpiod(ctx);
 
-	i2c_of_probe_simple_disable_regulator(dev, ctx);
+	i2c_of_probe_simple_disable_regulator(dev, ctx, true);
 	i2c_of_probe_simple_put_supply(ctx);
 }
 EXPORT_SYMBOL_NS_GPL(i2c_of_probe_simple_cleanup, "I2C_OF_PROBER");
-- 
2.55.0.rc0.799.gd6f94ed593-goog