[PATCH] Input: tca8418 - enable interrupt after it has been requested

[Damien Riegel <damien.riegel@savoirfairelinux.com>]

Currently, enabling keypad interrupts is one of the first operations
done on the keypad, even before the interrupt is requested, so there is
a small time window where the keypad can fire interrupts but the driver
is not yet ready to handle them. It's fine for level interrupts because
they will be handled anyway, but not so much for edge ones.

This commit modifies and moves the function in charge of configuring the
keypad. Enabling interrupts is now the last thing done on the keypad,
and after the interrupt has been requested by the driver.

Writing to the config register was also used to determine if the device
was indeed present on the bus or not, this has been replaced by reading
the lock/event count register to keep the same functionality.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
---
I originally made this patch on top of:

    800e3b9a6801 Input: drop owner assignment from i2c_driver

But I only compile-tested it on top of input/next. The issue was spotted
thanks to a bootloader that left the keypad configured, only with
interrupts disabled. So any button pressed or released during Linux's
boot was queued and triggered an interrupt as soon as the driver enabled
interrupts. It would really be appreciated if someone could give this
patch a try.

 drivers/input/keyboard/tca8418_keypad.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
index e37e335e406f..6da607d3b811 100644
--- a/drivers/input/keyboard/tca8418_keypad.c
+++ b/drivers/input/keyboard/tca8418_keypad.c
@@ -234,14 +234,7 @@ static irqreturn_t tca8418_irq_handler(int irq, void *dev_id)
 static int tca8418_configure(struct tca8418_keypad *keypad_data,
 			     u32 rows, u32 cols)
 {
-	int reg, error;
-
-	/* Write config register, if this fails assume device not present */
-	error = tca8418_write_byte(keypad_data, REG_CFG,
-				CFG_INT_CFG | CFG_OVR_FLOW_IEN | CFG_KE_IEN);
-	if (error < 0)
-		return -ENODEV;
-
+	int reg, error = 0;
 
 	/* Assemble a mask for row and column registers */
 	reg  =  ~(~0 << rows);
@@ -257,6 +250,12 @@ static int tca8418_configure(struct tca8418_keypad *keypad_data,
 	error |= tca8418_write_byte(keypad_data, REG_DEBOUNCE_DIS2, reg >> 8);
 	error |= tca8418_write_byte(keypad_data, REG_DEBOUNCE_DIS3, reg >> 16);
 
+	if (error)
+		return error;
+
+	error = tca8418_write_byte(keypad_data, REG_CFG,
+				CFG_INT_CFG | CFG_OVR_FLOW_IEN | CFG_KE_IEN);
+
 	return error;
 }
 
@@ -268,6 +267,7 @@ static int tca8418_keypad_probe(struct i2c_client *client,
 	struct input_dev *input;
 	u32 rows = 0, cols = 0;
 	int error, row_shift, max_keys;
+	u8 reg;
 
 	/* Check i2c driver capabilities */
 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_BYTE)) {
@@ -301,10 +301,10 @@ static int tca8418_keypad_probe(struct i2c_client *client,
 	keypad_data->client = client;
 	keypad_data->row_shift = row_shift;
 
-	/* Initialize the chip or fail if chip isn't present */
-	error = tca8418_configure(keypad_data, rows, cols);
-	if (error < 0)
-		return error;
+	/* Read key lock register, if this fails assume device not present */
+	error = tca8418_read_byte(keypad_data, REG_KEY_LCK_EC, &reg);
+	if (error)
+		return -ENODEV;
 
 	/* Configure input device */
 	input = devm_input_allocate_device(dev);
@@ -340,6 +340,11 @@ static int tca8418_keypad_probe(struct i2c_client *client,
 		return error;
 	}
 
+	/* Initialize the chip */
+	error = tca8418_configure(keypad_data, rows, cols);
+	if (error < 0)
+		return error;
+
 	error = input_register_device(input);
 	if (error) {
 		dev_err(dev, "Unable to register input device, error: %d\n",
-- 
2.14.2