[PATCH] regmap: Fix i2c word access when using SMBus access functions

[Guenter Roeck <linux@roeck-us.net>]

SMBUs access functions assume that 16 bit values are formatted as
little endian numbers. The direct i2c access functions in regmap,
however, assume that 16 bit values are formatted as big endian numbers.
As a result, the current code returns different values if an i2c chip's
16 bit registers are accessed through i2c access functions vs. SMBus
access functions.

Use regmap_smbus_read_word_swapped and regmap_smbus_write_word_swapped
for 16 bit SMBus accesses unless a chip is registered with val_format_endian
set to REGMAP_ENDIAN_LITTLE. In the latter case, keep using
regmap_smbus_write_word_data and regmap_smbus_read_word_data.

Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
Might be a candidate for -stable, though as far as I can see there is currently
no driver in the upstream kernel using regmap for 16-bit i2c accesses.

 drivers/base/regmap/regmap-i2c.c | 41 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c
index 053150a..865f4f8 100644
--- a/drivers/base/regmap/regmap-i2c.c
+++ b/drivers/base/regmap/regmap-i2c.c
@@ -87,6 +87,42 @@ static struct regmap_bus regmap_smbus_word = {
 	.reg_read = regmap_smbus_word_reg_read,
 };
 
+static int regmap_smbus_word_read_swapped(void *context, unsigned int reg,
+					  unsigned int *val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	if (reg > 0xff)
+		return -EINVAL;
+
+	ret = i2c_smbus_read_word_swapped(i2c, reg);
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+
+	return 0;
+}
+
+static int regmap_smbus_word_write_swapped(void *context, unsigned int reg,
+					   unsigned int val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (val > 0xffff || reg > 0xff)
+		return -EINVAL;
+
+	return i2c_smbus_write_word_swapped(i2c, reg, val);
+}
+
+static struct regmap_bus regmap_smbus_word_swapped = {
+	.reg_write = regmap_smbus_word_write_swapped,
+	.reg_read = regmap_smbus_word_read_swapped,
+};
+
 static int regmap_i2c_write(void *context, const void *data, size_t count)
 {
 	struct device *dev = context;
@@ -180,7 +216,10 @@ static const struct regmap_bus *regmap_get_i2c_bus(struct i2c_client *i2c,
 	else if (config->val_bits == 16 && config->reg_bits == 8 &&
 		 i2c_check_functionality(i2c->adapter,
 					 I2C_FUNC_SMBUS_WORD_DATA))
-		return &regmap_smbus_word;
+			if (config->val_format_endian == REGMAP_ENDIAN_LITTLE)
+				return &regmap_smbus_word;
+			else
+				return &regmap_smbus_word_swapped;
 	else if (config->val_bits == 8 && config->reg_bits == 8 &&
 		 i2c_check_functionality(i2c->adapter,
 					 I2C_FUNC_SMBUS_BYTE_DATA))
-- 
2.1.0