[PATCH 2/4] [media] em28xx: reduce stack usage in probe functions

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The two i2c probe functions use a lot of stack since they put
an i2c_client structure in a local variable:

drivers/media/usb/em28xx/em28xx-camera.c: In function 'em28xx_probe_sensor_micron':
drivers/media/usb/em28xx/em28xx-camera.c:205:1: error: the frame size of 1256 bytes is larger than 1152 bytes [-Werror=frame-larger-than=]
drivers/media/usb/em28xx/em28xx-camera.c: In function 'em28xx_probe_sensor_omnivision':
drivers/media/usb/em28xx/em28xx-camera.c:317:1: error: the frame size of 1248 bytes is larger than 1152 bytes [-Werror=frame-larger-than=]

This cleans up both of the above by removing the need for those
structures, calling the lower-level i2c function directly.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/media/usb/em28xx/em28xx-camera.c | 87 ++++++++++++++++++--------------
 1 file changed, 50 insertions(+), 37 deletions(-)

diff --git a/drivers/media/usb/em28xx/em28xx-camera.c b/drivers/media/usb/em28xx/em28xx-camera.c
index 89c890ba7dd6..e64940f95a91 100644
--- a/drivers/media/usb/em28xx/em28xx-camera.c
+++ b/drivers/media/usb/em28xx/em28xx-camera.c
@@ -99,6 +99,25 @@ static int em28xx_initialize_mt9m001(struct em28xx *dev)
 	return 0;
 }
 
+/* NOTE: i2c_smbus_read_word_data() doesn't work with BE data */
+static int em28xx_i2c_read_chip_id(struct em28xx *dev, u16 addr, u8 reg, void *buf)
+{
+	struct i2c_client *client = &dev->i2c_client[dev->def_i2c_bus];
+	struct i2c_msg msg[2];
+
+	msg[0].addr = addr;
+	msg[0].flags = client->flags & I2C_M_TEN;
+	msg[0].len = 1;
+	msg[0].buf = &reg;
+	msg[1].addr = addr;
+	msg[1].flags = client->flags & I2C_M_TEN;
+	msg[1].flags |= I2C_M_RD;
+	msg[1].len = 2;
+	msg[1].buf = buf;
+
+	return i2c_transfer(client->adapter, msg, 2);
+}
+
 /*
  * Probes Micron sensors with 8 bit address and 16 bit register width
  */
@@ -106,48 +125,29 @@ static int em28xx_probe_sensor_micron(struct em28xx *dev)
 {
 	int ret, i;
 	char *name;
-	u8 reg;
 	__be16 id_be;
+	u16 addr;
 	u16 id;
 
-	struct i2c_client client = dev->i2c_client[dev->def_i2c_bus];
-
 	dev->em28xx_sensor = EM28XX_NOSENSOR;
 	for (i = 0; micron_sensor_addrs[i] != I2C_CLIENT_END; i++) {
-		client.addr = micron_sensor_addrs[i];
-		/* NOTE: i2c_smbus_read_word_data() doesn't work with BE data */
+		addr = micron_sensor_addrs[i];
 		/* Read chip ID from register 0x00 */
-		reg = 0x00;
-		ret = i2c_master_send(&client, &reg, 1);
+		ret = em28xx_i2c_read_chip_id(dev, addr, 0x00, &id_be);
 		if (ret < 0) {
 			if (ret != -ENXIO)
 				dev_err(&dev->intf->dev,
 					"couldn't read from i2c device 0x%02x: error %i\n",
-				       client.addr << 1, ret);
-			continue;
-		}
-		ret = i2c_master_recv(&client, (u8 *)&id_be, 2);
-		if (ret < 0) {
-			dev_err(&dev->intf->dev,
-				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
+				       addr << 1, ret);
 			continue;
 		}
 		id = be16_to_cpu(id_be);
 		/* Read chip ID from register 0xff */
-		reg = 0xff;
-		ret = i2c_master_send(&client, &reg, 1);
+		ret = em28xx_i2c_read_chip_id(dev, addr, 0xff, &id_be);
 		if (ret < 0) {
 			dev_err(&dev->intf->dev,
 				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
-			continue;
-		}
-		ret = i2c_master_recv(&client, (u8 *)&id_be, 2);
-		if (ret < 0) {
-			dev_err(&dev->intf->dev,
-				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
+				addr << 1, ret);
 			continue;
 		}
 		/* Validate chip ID to be sure we have a Micron device */
@@ -197,13 +197,26 @@ static int em28xx_probe_sensor_micron(struct em28xx *dev)
 			dev_info(&dev->intf->dev,
 				 "sensor %s detected\n", name);
 
-		dev->i2c_client[dev->def_i2c_bus].addr = client.addr;
+		dev->i2c_client[dev->def_i2c_bus].addr = addr;
 		return 0;
 	}
 
 	return -ENODEV;
 }
 
+/* like i2c_smbus_read_byte_data, but allows passing an addr */
+static int em28xx_smbus_read_byte(struct em28xx *dev, u16 addr, u8 command)
+{
+	struct i2c_client *client = &dev->i2c_client[dev->def_i2c_bus];
+	union i2c_smbus_data data;
+	int status;
+
+	status = i2c_smbus_xfer(client->adapter, addr, client->flags,
+				I2C_SMBUS_READ, command,
+				I2C_SMBUS_BYTE_DATA, &data);
+	return (status < 0) ? status : data.byte;
+}
+
 /*
  * Probes Omnivision sensors with 8 bit address and register width
  */
@@ -212,31 +225,31 @@ static int em28xx_probe_sensor_omnivision(struct em28xx *dev)
 	int ret, i;
 	char *name;
 	u8 reg;
+	u16 addr;
 	u16 id;
-	struct i2c_client client = dev->i2c_client[dev->def_i2c_bus];
 
 	dev->em28xx_sensor = EM28XX_NOSENSOR;
 	/* NOTE: these devices have the register auto incrementation disabled
 	 * by default, so we have to use single byte reads !              */
 	for (i = 0; omnivision_sensor_addrs[i] != I2C_CLIENT_END; i++) {
-		client.addr = omnivision_sensor_addrs[i];
+		addr = omnivision_sensor_addrs[i];
 		/* Read manufacturer ID from registers 0x1c-0x1d (BE) */
 		reg = 0x1c;
-		ret = i2c_smbus_read_byte_data(&client, reg);
+		ret = em28xx_smbus_read_byte(dev, addr, reg);
 		if (ret < 0) {
 			if (ret != -ENXIO)
 				dev_err(&dev->intf->dev,
 					"couldn't read from i2c device 0x%02x: error %i\n",
-					client.addr << 1, ret);
+					addr << 1, ret);
 			continue;
 		}
 		id = ret << 8;
 		reg = 0x1d;
-		ret = i2c_smbus_read_byte_data(&client, reg);
+		ret = em28xx_smbus_read_byte(dev, addr, reg);
 		if (ret < 0) {
 			dev_err(&dev->intf->dev,
 				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
+				addr << 1, ret);
 			continue;
 		}
 		id += ret;
@@ -245,20 +258,20 @@ static int em28xx_probe_sensor_omnivision(struct em28xx *dev)
 			continue;
 		/* Read product ID from registers 0x0a-0x0b (BE) */
 		reg = 0x0a;
-		ret = i2c_smbus_read_byte_data(&client, reg);
+		ret = em28xx_smbus_read_byte(dev, addr, reg);
 		if (ret < 0) {
 			dev_err(&dev->intf->dev,
 				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
+				addr << 1, ret);
 			continue;
 		}
 		id = ret << 8;
 		reg = 0x0b;
-		ret = i2c_smbus_read_byte_data(&client, reg);
+		ret = em28xx_smbus_read_byte(dev, addr, reg);
 		if (ret < 0) {
 			dev_err(&dev->intf->dev,
 				"couldn't read from i2c device 0x%02x: error %i\n",
-				client.addr << 1, ret);
+				addr << 1, ret);
 			continue;
 		}
 		id += ret;
@@ -309,7 +322,7 @@ static int em28xx_probe_sensor_omnivision(struct em28xx *dev)
 			dev_info(&dev->intf->dev,
 				 "sensor %s detected\n", name);
 
-		dev->i2c_client[dev->def_i2c_bus].addr = client.addr;
+		dev->i2c_client[dev->def_i2c_bus].addr = addr;
 		return 0;
 	}
 
-- 
2.9.0

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