drm/bridge: it6505: Add i2c api power on check

Use i2c bus to read/write when it6505 power off will occur i2c error.
Add this check will prevent i2c error when it6505 power off.
Signed-off-by: Pin-Yen Lin <treapking@chromium.org>
Signed-off-by: Allen Chen <allen.chen@ite.com.tw>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220715024910.12578-3-allen.chen@ite.com.tw

drivers/gpu/drm/bridge/ite-it6505.c

@@ -506,6 +506,9 @@ static int it6505_read(struct it6505 *it6505, unsigned int reg_addr)
 	int err;
 	struct device *dev = &it6505->client->dev;
 
+	if (!it6505->powered)
+		return -ENODEV;
+
 	err = regmap_read(it6505->regmap, reg_addr, &value);
 	if (err < 0) {
 		dev_err(dev, "read failed reg[0x%x] err: %d", reg_addr, err);
@@ -521,6 +524,9 @@ static int it6505_write(struct it6505 *it6505, unsigned int reg_addr,
 	int err;
 	struct device *dev = &it6505->client->dev;
 
+	if (!it6505->powered)
+		return -ENODEV;
+
 	err = regmap_write(it6505->regmap, reg_addr, reg_val);
 
 	if (err < 0) {
@@ -538,6 +544,9 @@ static int it6505_set_bits(struct it6505 *it6505, unsigned int reg,
 	int err;
 	struct device *dev = &it6505->client->dev;
 
+	if (!it6505->powered)
+		return -ENODEV;
+
 	err = regmap_update_bits(it6505->regmap, reg, mask, value);
 	if (err < 0) {
 		dev_err(dev, "write reg[0x%x] = 0x%x mask = 0x%x failed err %d",
@@ -2559,13 +2568,12 @@ static int it6505_poweron(struct it6505 *it6505)
 		usleep_range(10000, 20000);
 	}
 
+	it6505->powered = true;
 	it6505_reset_logic(it6505);
 	it6505_int_mask_enable(it6505);
 	it6505_init(it6505);
 	it6505_lane_off(it6505);
 
-	it6505->powered = true;
-
 	return 0;
 }