Previously, the at24 driver would bail out in the case of a 16-bit
addressable EEPROM attached to an SMBus controller. This is because
SMBus block reads and writes don't map to I2C multi-byte reads and
writes when the offset portion is 2 bytes.
Instead of bailing out, this patch settles for functioning with single
byte read SMBus cycles. Writes can be block or single-byte, depending on
SMBus controller features.
This patch introduces at24_smbus_read_byte_data to transparently handle
single-byte reads from 8-bit and 16-bit devices.
Functionality has been tested with the following devices:
AT24CM01 attached to Intel ISCH SMBus (1.8 KB/s)
AT24C512 attached to Intel I801 SMBus (1.4 KB/s)
Signed-off-by: Nate Case <nc...@xes-inc.com>
Signed-off-by: Aaron Sierra <asie...@xes-inc.com>
---
drivers/misc/eeprom/Kconfig | 4 +++-
drivers/misc/eeprom/at24.c | 40 +++++++++++++++++++++++++++++++++++-----
2 files changed, 38 insertions(+), 6 deletions(-)
diff --git a/drivers/misc/eeprom/Kconfig b/drivers/misc/eeprom/Kconfig
index 04f2e1f..bc79a44 100644
--- a/drivers/misc/eeprom/Kconfig
+++ b/drivers/misc/eeprom/Kconfig
@@ -22,7 +22,9 @@ config EEPROM_AT24
If you use this with an SMBus adapter instead of an I2C adapter,
full functionality is not available. Only smaller devices are
- supported (24c16 and below, max 4 kByte).
+ supported via block reads (24c16 and below, max 4 kByte).
+ Larger devices that use 16-bit addresses will only work with
+ individual byte reads, which is very slow.
This driver can also be built as a module. If so, the module
will be called at24.
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index b92ee6e..457f49c 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -134,6 +134,32 @@ MODULE_DEVICE_TABLE(i2c, at24_ids);
/*-------------------------------------------------------------------------*/
/*
+ * Read a byte from an AT24 device using SMBus cycles.
+ */
+static inline s32 at24_smbus_read_byte_data(struct at24_data *at24,
+ struct i2c_client *client, u16 offset)
+{
+ s32 res;
+
+ if (!(at24->chip.flags & AT24_FLAG_ADDR16))
+ return i2c_smbus_read_byte_data(client, offset);
+
+ /*
+ * Emulate I2C multi-byte read by using SMBus "write byte" and
+ * "receive byte". This isn't optimal since there is an
+ * unnecessary STOP involved, but it's the only way to
+ * work on many SMBus controllers when talking to EEPROMs
+ * with multi-byte addresses.
+ */
+ res = i2c_smbus_write_byte_data(client,
+ ((offset >> 8) & 0xff), (offset & 0xff));
+ if (res)
+ return res;
+
+ return i2c_smbus_read_byte(client);
+}
+
+/*
* Write a byte to an AT24 device using SMBus cycles.
*/
static inline s32 at24_smbus_write_byte_data(struct at24_data *at24,
@@ -290,7 +316,8 @@ static ssize_t at24_eeprom_read(struct at24_data *at24,
char *buf,
}
break;
case I2C_SMBUS_BYTE_DATA:
- status = i2c_smbus_read_byte_data(client, offset);
+ status = at24_smbus_read_byte_data(at24,
+ client, offset);
if (status >= 0) {
buf[0] = status;
status = count;
@@ -584,10 +611,13 @@ 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 (chip.flags & AT24_FLAG_ADDR16)
- return -EPFNOSUPPORT;
-
- if (i2c_check_functionality(client->adapter,
+ if (chip.flags & AT24_FLAG_ADDR16) {
+ /*
+ * This will be slow, but better than nothing
+ * (e.g. read @ 1.4 KiB/s).
+ */
+ use_smbus = I2C_SMBUS_BYTE_DATA;
+ } else 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,
--
1.9.1
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