regmap: Fix i2c word access when using SMBus access functions

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 if a chip is configured as REGMAP_ENDIAN_BIG.
If the chip is configured as REGMAP_ENDIAN_LITTLE, keep using
regmap_smbus_write_word_data and regmap_smbus_read_word_data. Otherwise
reject registration if the controller does not support direct i2c accesses.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 45 insertions, 1 deletions

diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c
index 053150a7f9f2..4b76e33110a2 100644
--- a/drivers/base/regmap/regmap-i2c.c
+++ b/drivers/base/regmap/regmap-i2c.c
@@ -14,6 +14,7 @@
 #include <linux/i2c.h>
 #include <linux/module.h>
 
+#include "internal.h"
 
 static int regmap_smbus_byte_reg_read(void *context, unsigned int reg,
                                       unsigned int *val)
@@ -87,6 +88,42 @@ 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 +217,14 @@ 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;
+                switch (regmap_get_val_endian(&i2c->dev, NULL, config)) {
+                case REGMAP_ENDIAN_LITTLE:
+                        return &regmap_smbus_word;
+                case REGMAP_ENDIAN_BIG:
+                        return &regmap_smbus_word_swapped;
+                default:                /* everything else is not supported */
+                        break;
+                }
         else if (config->val_bits == 8 && config->reg_bits == 8 &&
                  i2c_check_functionality(i2c->adapter,
                                          I2C_FUNC_SMBUS_BYTE_DATA))