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

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

[Mark Brown]

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>
---
 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

[PATCH 2/3] mfd: Push byte swap out of WM8994 bulk I/O

[Mark Brown]

For bulk I/O it is both convenient and more sensible to pre-swap the data
rather than doing the swap as part of the I/O operation so move the byte
swaps we're currently doing into the core write function into the register
based functions, giving the bulk write function a straight pass through
to the chip.

This leaves reads inconsistent, this will be addressed as a followup patch.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
---
 drivers/mfd/wm8994-core.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index ce93796..475bd50 100644
--- a/drivers/mfd/wm8994-core.c
+++ b/drivers/mfd/wm8994-core.c
@@ -107,9 +107,7 @@ static int wm8994_write(struct wm8994 *wm8994, unsigned short reg,
 
 	for (i = 0; i < bytes / 2; i++) {
 		dev_vdbg(wm8994->dev, "Write %04x to R%d(0x%x)\n",
-			 buf[i], reg + i, reg + i);
-
-		buf[i] = cpu_to_be16(buf[i]);
+			 be16_to_cpu(buf[i]), reg + i, reg + i);
 	}
 
 	return wm8994->write_dev(wm8994, reg, bytes, src);
@@ -127,6 +125,8 @@ int wm8994_reg_write(struct wm8994 *wm8994, unsigned short reg,
 {
 	int ret;
 
+	val = cpu_to_be16(val);
+
 	mutex_lock(&wm8994->io_lock);
 
 	ret = wm8994_write(wm8994, reg, 2, &val);
@@ -143,7 +143,7 @@ EXPORT_SYMBOL_GPL(wm8994_reg_write);
  * @wm8994: Device to write to
  * @reg: First register
  * @count: Number of registers
- * @buf: Buffer to write from.
+ * @buf: Buffer to write from.  Data must be big-endian formatted.
  */
 int wm8994_bulk_write(struct wm8994 *wm8994, unsigned short reg,
 		      int count, u16 *buf)
@@ -183,6 +183,8 @@ int wm8994_set_bits(struct wm8994 *wm8994, unsigned short reg,
 	r &= ~mask;
 	r |= val;
 
+	r = cpu_to_be16(r);
+
 	ret = wm8994_write(wm8994, reg, 2, &r);
 
 out:
-- 
1.7.4.1

[PATCH 3/3] mfd: Constify WM8994 write path

[Mark Brown]

Allow const buffers to be passed in without type safety issues.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
---
 drivers/mfd/wm8994-core.c       |    8 ++++----
 include/linux/mfd/wm8994/core.h |    4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index 475bd50..3f5b7cc 100644
--- a/drivers/mfd/wm8994-core.c
+++ b/drivers/mfd/wm8994-core.c
@@ -97,9 +97,9 @@ int wm8994_bulk_read(struct wm8994 *wm8994, unsigned short reg,
 EXPORT_SYMBOL_GPL(wm8994_bulk_read);
 
 static int wm8994_write(struct wm8994 *wm8994, unsigned short reg,
-			int bytes, void *src)
+			int bytes, const void *src)
 {
-	u16 *buf = src;
+	const u16 *buf = src;
 	int i;
 
 	BUG_ON(bytes % 2);
@@ -146,7 +146,7 @@ EXPORT_SYMBOL_GPL(wm8994_reg_write);
  * @buf: Buffer to write from.  Data must be big-endian formatted.
  */
 int wm8994_bulk_write(struct wm8994 *wm8994, unsigned short reg,
-		      int count, u16 *buf)
+		      int count, const u16 *buf)
 {
 	int ret;
 
@@ -583,7 +583,7 @@ static int wm8994_i2c_read_device(struct wm8994 *wm8994, unsigned short reg,
 }
 
 static int wm8994_i2c_write_device(struct wm8994 *wm8994, unsigned short reg,
-				   int bytes, void *src)
+				   int bytes, const void *src)
 {
 	struct i2c_client *i2c = wm8994->control_data;
 	struct i2c_msg xfer[2];
diff --git a/include/linux/mfd/wm8994/core.h b/include/linux/mfd/wm8994/core.h
index cb7d3ae..f0b69cd 100644
--- a/include/linux/mfd/wm8994/core.h
+++ b/include/linux/mfd/wm8994/core.h
@@ -59,7 +59,7 @@ struct wm8994 {
 	int (*read_dev)(struct wm8994 *wm8994, unsigned short reg,
 			int bytes, void *dest);
 	int (*write_dev)(struct wm8994 *wm8994, unsigned short reg,
-			 int bytes, void *src);
+			 int bytes, const void *src);
 
 	void *control_data;
 
@@ -89,7 +89,7 @@ int wm8994_set_bits(struct wm8994 *wm8994, unsigned short reg,
 int wm8994_bulk_read(struct wm8994 *wm8994, unsigned short reg,
 		     int count, u16 *buf);
 int wm8994_bulk_write(struct wm8994 *wm8994, unsigned short reg,
-		     int count, u16 *buf);
+		     int count, const u16 *buf);
 
 
 /* Helper to save on boilerplate */
-- 
1.7.4.1

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

[Samuel Ortiz]

Hi Mark,

On Thu, Mar 17, 2011 at 09:42:28PM +0000, Mark Brown wrote:
> 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.
All 3 patches applied, thanks.

Cheers,
Samuel.

-- 
Intel Open Source Technology Centre
http://oss.intel.com/