The I2C specification explicitly describes both SDA and SCL as
bidirectional lines. An I2C master with a read-only SCL is thus not
compliant. If a slow slave stretches the clock, errors will happen,
so the bus can't be considered as reliable.
Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
---
drivers/i2c/algos/i2c-algo-bit.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- linux-2.6.37-rc5.orig/drivers/i2c/algos/i2c-algo-bit.c 2010-12-07 11:02:38.000000000 +0100
+++ linux-2.6.37-rc5/drivers/i2c/algos/i2c-algo-bit.c 2010-12-07 11:03:23.000000000 +0100
@@ -604,9 +604,10 @@ static int __i2c_bit_add_bus(struct i2c_
int (*add_adapter)(struct i2c_adapter *))
{
struct i2c_algo_bit_data *bit_adap = adap->algo_data;
+ int ret;
if (bit_test) {
- int ret = test_bus(bit_adap, adap->name);
+ ret = test_bus(bit_adap, adap->name);
if (ret < 0)
return -ENODEV;
}
@@ -615,7 +616,16 @@ static int __i2c_bit_add_bus(struct i2c_
adap->algo = &i2c_bit_algo;
adap->retries = 3;
- return add_adapter(adap);
+ ret = add_adapter(adap);
+ if (ret < 0)
+ return ret;
+
+ /* Complain if SCL can't be read */
+ if (bit_adap->getscl == NULL) {
+ dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
+ dev_warn(&adap->dev, "Bus may be unreliable\n");
+ }
+ return 0;
}
int i2c_bit_add_bus(struct i2c_adapter *adap)
--
Jean Delvare
--
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