gpio: sx150x: correct and refine reset-on-probe behavior

Replace the arbitrary software-reset call from the device-probe
method, because:

- It is defective.  To work correctly, it should be two byte writes,
  not a single word write.  As it stands, it does nothing.

- Some devices with sx150x expanders installed have their NRESET pins
  ganged on the same line, so resetting one causes the others to reset -
  not a nice thing to do arbitrarily!

- The probe, usually taking place at boot, implies a recent hard-reset,
  so a software reset at this point is just a waste of energy anyway.

Therefore, make it optional, defaulting to off, as this will match the
common case of probing at powerup and also matches the current broken
no-op behavior.

Signed-off-by: Gregory Bean <gbean@codeaurora.org>
Reviewed-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpio/sx150x.c

@@ -459,16 +459,32 @@ static int sx150x_init_io(struct sx150x_chip *chip, u8 base, u16 cfg)
 	return err;
 }
 
+static int sx150x_reset(struct sx150x_chip *chip)
+{
+	int err;
+
+	err = i2c_smbus_write_byte_data(chip->client,
+					chip->dev_cfg->reg_reset,
+					0x12);
+	if (err < 0)
+		return err;
+
+	err = i2c_smbus_write_byte_data(chip->client,
+					chip->dev_cfg->reg_reset,
+					0x34);
+	return err;
+}
+
 static int sx150x_init_hw(struct sx150x_chip *chip,
 			struct sx150x_platform_data *pdata)
 {
 	int err = 0;
 
-	err = i2c_smbus_write_word_data(chip->client,
+	if (pdata->reset_during_probe) {
-					chip->dev_cfg->reg_reset,
+		err = sx150x_reset(chip);
-					0x3412);
 		if (err < 0)
 			return err;
+	}
 
 	err = sx150x_i2c_write(chip->client,
 			chip->dev_cfg->reg_misc,

include/linux/i2c/sx150x.h

@@ -63,6 +63,9 @@
  *            IRQ lines will appear.  Similarly to gpio_base, the expander
  *            will create a block of irqs beginning at this number.
  *            This value is ignored if irq_summary is < 0.
+ * @reset_during_probe: If set to true, the driver will trigger a full
+ *                      reset of the chip at the beginning of the probe
+ *                      in order to place it in a known state.
  */
 struct sx150x_platform_data {
 	unsigned gpio_base;
@@ -73,6 +76,7 @@ struct sx150x_platform_data {
 	u16      io_polarity;
 	int      irq_summary;
 	unsigned irq_base;
+	bool     reset_during_probe;
 };
 
 #endif /* __LINUX_I2C_SX150X_H */