eeprom: at24: extend driver to allow writing via i2c_smbus_write_byte_data

I have a at24 EEPROM connected via i2c bus provided by ISCH i2c
bus driver. This bus driver does not support
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK and so I was looking for a way
to be able to write the eeprom. This patch adds support for
I2C_SMBUS_BYTE_DATA writing via i2c_smbus_write_byte_data.
It is quite slow, but it works.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
[wsa: s/use_smbuse_write/use_smbus_write/]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 29 insertions, 6 deletions

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index d87f77f790d6..2d3db81be099 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -56,6 +56,7 @@ struct at24_data {
         struct at24_platform_data chip;
         struct memory_accessor macc;
         int use_smbus;
+        int use_smbus_write;
 
         /*
          * Lock protects against activities from other Linux tasks,
@@ -324,7 +325,7 @@ static ssize_t at24_eeprom_write(struct at24_data *at24, const char *buf,
 {
         struct i2c_client *client;
         struct i2c_msg msg;
-        ssize_t status;
+        ssize_t status = 0;
         unsigned long timeout, write_time;
         unsigned next_page;
 
@@ -365,9 +366,18 @@ static ssize_t at24_eeprom_write(struct at24_data *at24, const char *buf,
         timeout = jiffies + msecs_to_jiffies(write_timeout);
         do {
                 write_time = jiffies;
-                if (at24->use_smbus) {
-                        status = i2c_smbus_write_i2c_block_data(client,
-                                        offset, count, buf);
+                if (at24->use_smbus_write) {
+                        switch (at24->use_smbus_write) {
+                        case I2C_SMBUS_I2C_BLOCK_DATA:
+                                status = i2c_smbus_write_i2c_block_data(client,
+                                                offset, count, buf);
+                                break;
+                        case I2C_SMBUS_BYTE_DATA:
+                                status = i2c_smbus_write_byte_data(client,
+                                                offset, buf[0]);
+                                break;
+                        }
+
                         if (status == 0)
                                 status = count;
                 } else {
@@ -487,6 +497,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
         struct at24_platform_data chip;
         bool writable;
         int use_smbus = 0;
+        int use_smbus_write = 0;
         struct at24_data *at24;
         int err;
         unsigned i, num_addresses;
@@ -546,6 +557,18 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
                 }
         }
 
+        /* Use I2C operations unless we're stuck with SMBus extensions. */
+        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
+                if (i2c_check_functionality(client->adapter,
+                                I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
+                        use_smbus_write = I2C_SMBUS_I2C_BLOCK_DATA;
+                } else if (i2c_check_functionality(client->adapter,
+                                I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {
+                        use_smbus_write = I2C_SMBUS_BYTE_DATA;
+                        chip.page_size = 1;
+                }
+        }
+
         if (chip.flags & AT24_FLAG_TAKE8ADDR)
                 num_addresses = 8;
         else
@@ -559,6 +582,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 
         mutex_init(&at24->lock);
         at24->use_smbus = use_smbus;
+        at24->use_smbus_write = use_smbus_write;
         at24->chip = chip;
         at24->num_addresses = num_addresses;
 
@@ -576,8 +600,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 
         writable = !(chip.flags & AT24_FLAG_READONLY);
         if (writable) {
-                if (!use_smbus || i2c_check_functionality(client->adapter,
-                                I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
+                if (!use_smbus || use_smbus_write) {
 
                         unsigned write_max = chip.page_size;