Re: [PATCH V2] input:ad7879-i2c use swapped varient of i2c_smbus_read_word_data

On 10/21/11 17:09, Dmitry Torokhov wrote:

On Fri, Oct 21, 2011 at 12:57:16PM +0100, Jonathan Cameron wrote:

quoted

This varient was introduced in
i2c: boilerplate function for byte swapped smbus_write/read_word_data

This also has the side effect of ensuring any errors from the i2c
read and no longer mangled.

Signed-off-by: Jonathan Cameron <redacted>
---
V2: include the write function as pointed out by Michael Hennerich.

The patch introducing this swapped function is working its way through the i2c
tree.

 drivers/input/touchscreen/ad7879-i2c.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/touchscreen/ad7879-i2c.c b/drivers/input/touchscreen/ad7879-i2c.c
index 4e4e58c..cc51392 100644
--- a/drivers/input/touchscreen/ad7879-i2c.c
+++ b/drivers/input/touchscreen/ad7879-i2c.c

@@ -47,7 +47,7 @@ static int ad7879_i2c_read(struct device *dev, u8 reg)
 {
 	struct i2c_client *client = to_i2c_client(dev);
 
-	return swab16(i2c_smbus_read_word_data(client, reg));
+	return i2c_smbus_read_word_swapped(client, reg);

This is still not endian-safe. I wonder if introducing
i2c_smbus_read_word_swapped() just makes the metter worse by hiding
this...

I'd prefer if we had i2c_smbus_read_be16() instead.

smbus spec says that all transfers must be little endian.
Hence it is type safe because the smbus controllers are guaranteed to have made
that assumption and converted to cpu endianess.  If not they are buggy.
Hence, this is endian safe.

Unfortunately numerous devices do the exact opposite (for successive approximation
ADCs it would be silly to do otherwise.) Hence they use the smbus protocol, but
then have to flip the bytes.