diff options
| -rw-r--r-- | Documentation/i2c/chips/pcf8574 | 8 | ||||
| -rw-r--r-- | drivers/i2c/chips/pcf8574.c | 14 |
2 files changed, 10 insertions, 12 deletions
diff --git a/Documentation/i2c/chips/pcf8574 b/Documentation/i2c/chips/pcf8574 index 2752c8c..5c1ad13 100644 --- a/Documentation/i2c/chips/pcf8574 +++ b/Documentation/i2c/chips/pcf8574 @@ -62,8 +62,6 @@ if the corresponding output is set as 1, otherwise the current output value, that is to say 0. The write file is read/write. Writing a value outputs it on the I/O -port. Reading returns the last written value. - -On module initialization the chip is configured as eight inputs (all -outputs to 1), so you can connect any circuit to the PCF8574(A) without -being afraid of short-circuit. +port. Reading returns the last written value. As it is not possible +to read this value from the chip, you need to write at least once to +this file before you can read back from it. diff --git a/drivers/i2c/chips/pcf8574.c b/drivers/i2c/chips/pcf8574.c index 32b2542..21c6dd6 100644 --- a/drivers/i2c/chips/pcf8574.c +++ b/drivers/i2c/chips/pcf8574.c @@ -48,14 +48,11 @@ static unsigned short normal_i2c[] = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, /* Insmod parameters */ I2C_CLIENT_INSMOD_2(pcf8574, pcf8574a); -/* Initial values */ -#define PCF8574_INIT 255 /* All outputs on (input mode) */ - /* Each client has this additional data */ struct pcf8574_data { struct i2c_client client; - u8 write; /* Remember last written value */ + int write; /* Remember last written value */ }; static int pcf8574_attach_adapter(struct i2c_adapter *adapter); @@ -85,7 +82,11 @@ static DEVICE_ATTR(read, S_IRUGO, show_read, NULL); static ssize_t show_write(struct device *dev, struct device_attribute *attr, char *buf) { struct pcf8574_data *data = i2c_get_clientdata(to_i2c_client(dev)); - return sprintf(buf, "%u\n", data->write); + + if (data->write < 0) + return data->write; + + return sprintf(buf, "%d\n", data->write); } static ssize_t set_write(struct device *dev, struct device_attribute *attr, const char *buf, @@ -206,8 +207,7 @@ static int pcf8574_detach_client(struct i2c_client *client) static void pcf8574_init_client(struct i2c_client *client) { struct pcf8574_data *data = i2c_get_clientdata(client); - data->write = PCF8574_INIT; - i2c_smbus_write_byte(client, data->write); + data->write = -EAGAIN; } static int __init pcf8574_init(void) |