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authorJean Delvare <khali@linux-fr.org>2010-05-21 18:40:57 +0200
committerJean Delvare <khali@linux-fr.org>2010-05-21 18:40:57 +0200
commit7aeb96642f70139a194d685b132605836f6f8dbb (patch)
tree16ff60fcd074e8b2efb052d883175b48f56b80bb /drivers/misc/eeprom
parentc5aa69285c573e42042530be86b7af6f5fe9e240 (diff)
at24: Fall back to byte or word reads if needed
Increase the portability of the at24 driver by letting it read from EEPROM chips connected to cheap SMBus controllers that support neither raw I2C messages nor even I2C block reads. All SMBus controllers should support either word reads or byte reads, so read support becomes universal, much like with the legacy "eeprom" driver. Obviously, this only works with EEPROM chips up to AT24C16, that use 8-bit offset addressing. 16-bit offset addressing is almost impossible to support on SMBus controllers. I did not add universal support for writes, as I had no immediate need for this, but it could be added later if needed (with the same performance issue as byte and word reads have, of course.) Signed-off-by: Jean Delvare <khali@linux-fr.org> Reviewed-by: Wolfram Sang <w.sang@pengutronix.de> Cc: Konstantin Lazarev <klazarev@sbcglobal.net>
Diffstat (limited to 'drivers/misc/eeprom')
-rw-r--r--drivers/misc/eeprom/at24.c59
1 files changed, 48 insertions, 11 deletions
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index db7d0f21b65..0c11e411d8e 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)