[PATCH v2] [media] adv7604: Add support for hardware reset

[Dragos Bogdan <dragos.bogdan@analog.com>]

The part can be reset by a low pulse on the RESET pin (i.e. a hardware
reset) with a minimum width of 5 ms. It is recommended to wait 5 ms
after the low pulse before an I2C write is performed to the part.
For safety reasons, the delays will be between 5 and 10 ms.

The RESET pin can be tied high, so the GPIO is optional.

Signed-off-by: Dragos Bogdan <dragos.bogdan@analog.com>
---
Changes since v1:
 - Replace mdelay() with usleep_range();
 - Limit the comments to 75 characters per line.

 drivers/media/i2c/adv7604.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/media/i2c/adv7604.c b/drivers/media/i2c/adv7604.c
index 41a1bfc..73c79bb 100644
--- a/drivers/media/i2c/adv7604.c
+++ b/drivers/media/i2c/adv7604.c
@@ -164,6 +164,7 @@ struct adv76xx_state {
 	struct adv76xx_platform_data pdata;
 
 	struct gpio_desc *hpd_gpio[4];
+	struct gpio_desc *reset_gpio;
 
 	struct v4l2_subdev sd;
 	struct media_pad pads[ADV76XX_PAD_MAX];
@@ -2996,6 +2997,21 @@ static int configure_regmaps(struct adv76xx_state *state)
 	return 0;
 }
 
+static int adv76xx_reset(struct adv76xx_state *state)
+{
+	if (state->reset_gpio) {
+		/* ADV76XX can be reset by a low reset pulse of minimum 5 ms. */
+		gpiod_set_value_cansleep(state->reset_gpio, 0);
+		usleep_range(5000, 10000);
+		gpiod_set_value_cansleep(state->reset_gpio, 1);
+		/* It is recommended to wait 5 ms after the low pulse before */
+		/* an I2C write is performed to the ADV76XX. */
+		usleep_range(5000, 10000);
+	}
+
+	return 0;
+}
+
 static int adv76xx_probe(struct i2c_client *client,
 			 const struct i2c_device_id *id)
 {
@@ -3059,6 +3075,12 @@ static int adv76xx_probe(struct i2c_client *client,
 		if (state->hpd_gpio[i])
 			v4l_info(client, "Handling HPD %u GPIO\n", i);
 	}
+	state->reset_gpio = devm_gpiod_get_optional(&client->dev, "reset",
+								GPIOD_OUT_HIGH);
+	if (IS_ERR(state->reset_gpio))
+		return PTR_ERR(state->reset_gpio);
+
+	adv76xx_reset(state);
 
 	state->timings = cea640x480;
 	state->format = adv76xx_format_info(state, MEDIA_BUS_FMT_YUYV8_2X8);
-- 
2.1.4