1 files changed, 48 insertions, 11 deletions

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index db7d0f21b65d..0c11e411d8ec 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -54,7 +54,7 @@
 struct at24_data {
         struct at24_platform_data chip;
         struct memory_accessor macc;
-        bool use_smbus;
+        int use_smbus;
 
         /*
          * Lock protects against activities from other Linux tasks,
@@ -184,11 +184,19 @@ static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
         if (count > io_limit)
                 count = io_limit;
 
-        if (at24->use_smbus) {
+        switch (at24->use_smbus) {
+        case I2C_SMBUS_I2C_BLOCK_DATA:
                 /* Smaller eeproms can work given some SMBus extension calls */
                 if (count > I2C_SMBUS_BLOCK_MAX)
                         count = I2C_SMBUS_BLOCK_MAX;
-        } else {
+                break;
+        case I2C_SMBUS_WORD_DATA:
+                count = 2;
+                break;
+        case I2C_SMBUS_BYTE_DATA:
+                count = 1;
+                break;
+        default:
                 /*
                  * When we have a better choice than SMBus calls, use a
                  * combined I2C message. Write address; then read up to
@@ -219,10 +227,27 @@ static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
         timeout = jiffies + msecs_to_jiffies(write_timeout);
         do {
                 read_time = jiffies;
-                if (at24->use_smbus) {
+                switch (at24->use_smbus) {
+                case I2C_SMBUS_I2C_BLOCK_DATA:
                         status = i2c_smbus_read_i2c_block_data(client, offset,
                                         count, buf);
-                } else {
+                        break;
+                case I2C_SMBUS_WORD_DATA:
+                        status = i2c_smbus_read_word_data(client, offset);
+                        if (status >= 0) {
+                                buf[0] = status & 0xff;
+                                buf[1] = status >> 8;
+                                status = count;
+                        }
+                        break;
+                case I2C_SMBUS_BYTE_DATA:
+                        status = i2c_smbus_read_byte_data(client, offset);
+                        if (status >= 0) {
+                                buf[0] = status;
+                                status = count;
+                        }
+                        break;
+                default:
                         status = i2c_transfer(client->adapter, msg, 2);
                         if (status == 2)
                                 status = count;
@@ -434,7 +459,7 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 {
         struct at24_platform_data chip;
         bool writable;
-        bool use_smbus = false;
+        int use_smbus = 0;
         struct at24_data *at24;
         int err;
         unsigned i, num_addresses;
@@ -475,12 +500,19 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
                         err = -EPFNOSUPPORT;
                         goto err_out;
                 }
-                if (!i2c_check_functionality(client->adapter,
+                if (i2c_check_functionality(client->adapter,
                                 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
+                        use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
+                } else if (i2c_check_functionality(client->adapter,
+                                I2C_FUNC_SMBUS_READ_WORD_DATA)) {
+                        use_smbus = I2C_SMBUS_WORD_DATA;
+                } else if (i2c_check_functionality(client->adapter,
+                                I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
+                        use_smbus = I2C_SMBUS_BYTE_DATA;
+                } else {
                         err = -EPFNOSUPPORT;
                         goto err_out;
                 }
-                use_smbus = true;
         }
 
         if (chip.flags & AT24_FLAG_TAKE8ADDR)
@@ -566,11 +598,16 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
         dev_info(&client->dev, "%zu byte %s EEPROM %s\n",
                 at24->bin.size, client->name,
                 writable ? "(writable)" : "(read-only)");
+        if (use_smbus == I2C_SMBUS_WORD_DATA ||
+            use_smbus == I2C_SMBUS_BYTE_DATA) {
+                dev_notice(&client->dev, "Falling back to %s reads, "
+                           "performance will suffer\n", use_smbus ==
+                           I2C_SMBUS_WORD_DATA ? "word" : "byte");
+        }
         dev_dbg(&client->dev,
-                "page_size %d, num_addresses %d, write_max %d%s\n",
+                "page_size %d, num_addresses %d, write_max %d, use_smbus %d\n",
                 chip.page_size, num_addresses,
-                at24->write_max,
-                use_smbus ? ", use_smbus" : "");
+                at24->write_max, use_smbus);
 
         /* export data to kernel code */
         if (chip.setup)