[PATCH 1/3] mfd: Avoid copying data in WM8994 I2C write

From: Mark Brown
Date: Thu Mar 17 2011 - 17:42:39 EST


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@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
---
drivers/mfd/wm8994-core.c | 22 +++++++++++++---------
1 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index 749c31d..ce93796 100644
--- 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 *)&reg;
+
+ 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;
--
1.7.4.1

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