mfd: Avoid copying data in WM8994 I2C write

As well as providing a trivial performance optimisation this also avoids
allocating a copy of the message on the stack which is beneficial when
doing large transfers.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index 749c31d29b09d89b20c8a3d39a58a52ddc95fc43..ce93796e7f5735f4cb319db6dc4d3c5bf69273fc 100644 (file)
--- a/drivers/mfd/wm8994-core.c
+++ b/drivers/mfd/wm8994-core.c
@@ -580,25 +580,29 @@ static int wm8994_i2c_read_device(struct wm8994 *wm8994, unsigned short reg,
        return 0;
 }
 
-/* Currently we allocate the write buffer on the stack; this is OK for
- * small writes - if we need to do large writes this will need to be
- * revised.
- */
 static int wm8994_i2c_write_device(struct wm8994 *wm8994, unsigned short reg,
                                   int bytes, void *src)
 {
        struct i2c_client *i2c = wm8994->control_data;
-       unsigned char msg[bytes + 2];
+       struct i2c_msg xfer[2];
        int ret;
 
        reg = cpu_to_be16(reg);
-       memcpy(&msg[0], &reg, 2);
-       memcpy(&msg[2], src, bytes);
 
-       ret = i2c_master_send(i2c, msg, bytes + 2);
+       xfer[0].addr = i2c->addr;
+       xfer[0].flags = 0;
+       xfer[0].len = 2;
+       xfer[0].buf = (char *)®
+
+       xfer[1].addr = i2c->addr;
+       xfer[1].flags = I2C_M_NOSTART;
+       xfer[1].len = bytes;
+       xfer[1].buf = (char *)src;
+
+       ret = i2c_transfer(i2c->adapter, xfer, 2);
        if (ret < 0)
                return ret;
-       if (ret < bytes + 2)
+       if (ret != 2)
                return -EIO;
 
        return 0;