[PATCH v2 1/7] Input: elan_i2c - Wait for initialization after enabling regulator supply

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

Elan trackpad controllers require some delay after enabling power to
the controller for the hardware and firmware to initialize:

  - 2ms for hardware initialization
  - 100ms for firmware initialization

Until then, the hardware will not respond to I2C transfers. This was
observed on the MT8173 Chromebooks after the regulator supply for the
trackpad was changed to "not always on".

Add proper delays after regulator_enable() calls. To avoid impacting
the boot time of existing devices that have the power rails always on,
skip the delay if the regulator supply was already enabled. In this
case the regulator is either always on, was on by default at power up,
or was left on by some other driver, such as the I2C OF component
prober. Either way the controller has had ample time to initialize.

Fixes: 6696777c6506 ("Input: add driver for Elan I2C/SMbus touchpad")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
Changes since v1:
- Delay only if the regulator was previously disabled / turned off
- Link to v1
  https://lore.kernel.org/all/20241001093815.2481899-1-wenst@chromium.org/
---
 drivers/input/mouse/elan_i2c_core.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
index f93dd545d66b..db48d7ef8357 100644
--- a/drivers/input/mouse/elan_i2c_core.c
+++ b/drivers/input/mouse/elan_i2c_core.c
@@ -47,6 +47,8 @@
 #define ETP_FWIDTH_REDUCE	90
 #define ETP_FINGER_WIDTH	15
 #define ETP_RETRY_COUNT		3
+/* H/W init 2 ms + F/W init 100 ms w/ round up */
+#define ETP_POWER_ON_DELAY	110
 
 /* quirks to control the device */
 #define ETP_QUIRK_QUICK_WAKEUP	BIT(0)
@@ -1219,6 +1221,7 @@ static int elan_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct elan_tp_data *data;
 	unsigned long irqflags;
+	bool supply_was_enabled;
 	int error;
 
 	if (IS_ENABLED(CONFIG_MOUSE_ELAN_I2C_I2C) &&
@@ -1250,6 +1253,8 @@ static int elan_probe(struct i2c_client *client)
 	if (IS_ERR(data->vcc))
 		return dev_err_probe(dev, PTR_ERR(data->vcc), "Failed to get 'vcc' regulator\n");
 
+	supply_was_enabled = regulator_is_enabled(data->vcc);
+
 	error = regulator_enable(data->vcc);
 	if (error) {
 		dev_err(dev, "Failed to enable regulator: %d\n", error);
@@ -1263,6 +1268,9 @@ static int elan_probe(struct i2c_client *client)
 		return error;
 	}
 
+	if (!supply_was_enabled)
+		msleep(ETP_POWER_ON_DELAY);
+
 	/* Make sure there is something at this address */
 	error = i2c_smbus_read_byte(client);
 	if (error < 0) {
@@ -1406,11 +1414,16 @@ static int elan_resume(struct device *dev)
 	int error;
 
 	if (!device_may_wakeup(dev)) {
+		bool supply_was_enabled = regulator_is_enabled(data->vcc);
+
 		error = regulator_enable(data->vcc);
 		if (error) {
 			dev_err(dev, "error %d enabling regulator\n", error);
 			goto err;
 		}
+
+		if (!supply_was_enabled)
+			msleep(ETP_POWER_ON_DELAY);
 	}
 
 	error = elan_set_power(data, true);
-- 
2.55.0.rc0.799.gd6f94ed593-goog