Introduce at24_smbus_write_byte_data() to allow very slow (e.g.
248 B/s) write access to 16-bit EEPROM devices attached to SMBus
controllers like the Intel SCH.
Signed-off-by: Nate Case <nc...@xes-inc.com>
Signed-off-by: Aaron Sierra <asie...@xes-inc.com>
---
v2 - Unchanged from v1
drivers/misc/eeprom/at24.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index c3d3add..32eca05 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -134,6 +134,25 @@ MODULE_DEVICE_TABLE(i2c, at24_ids);
/*-------------------------------------------------------------------------*/
/*
+ * Write a byte to an AT24 device using SMBus cycles.
+ */
+static inline s32 at24_smbus_write_byte_data(struct at24_data *at24,
+ struct i2c_client *client, u16 offset, u8 value)
+{
+ if (!(at24->chip.flags & AT24_FLAG_ADDR16))
+ return i2c_smbus_write_byte_data(client, offset, value);
+
+ /*
+ * Emulate I2C multi-byte write by using SMBus "write word"
+ * cycle. We split up the 16-bit offset among the "command"
+ * byte and the first data byte.
+ */
+ return i2c_smbus_write_word_data(client,
+ ((offset >> 8) & 0xff),
+ (value << 8) | (offset & 0xff));
+}
+
+/*
* Write block data to an AT24 device using SMBus cycles.
*/
static inline s32 at24_smbus_write_i2c_block_data(struct at24_data *at24,
@@ -376,8 +395,8 @@ static ssize_t at24_eeprom_write(struct at24_data *at24,
const char *buf,
client, offset, count, buf);
break;
case I2C_SMBUS_BYTE_DATA:
- status = i2c_smbus_write_byte_data(client,
- offset, buf[0]);
+ status = at24_smbus_write_byte_data(at24,
+ client, offset, buf[0]);
break;
}
@@ -562,7 +581,17 @@ static int at24_probe(struct i2c_client *client, const
struct i2c_device_id *id)
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,
+ } else if (chip.flags & AT24_FLAG_ADDR16 &&
+ i2c_check_functionality(client->adapter,
+ I2C_FUNC_SMBUS_WRITE_WORD_DATA)) {
+ /*
+ * We need SMBUS_WRITE_WORD_DATA to implement
+ * byte writes for 16-bit address devices.
+ */
+ use_smbus_write = I2C_SMBUS_BYTE_DATA;
+ chip.page_size = 1;
+ } else if (!(chip.flags & AT24_FLAG_ADDR16) &&
+ i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {
use_smbus_write = I2C_SMBUS_BYTE_DATA;
chip.page_size = 1;
--
1.9.1
--
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