i2c-algo-bit: Complain about masters which can't read SCL

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@linux-fr.org>

diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
index 938170b8998b8c835edec9113c217dae8c13f9a6..38319a69bd0a9de978fc688bded38fa3dea90def 100644 (file)
--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/drivers/i2c/algos/i2c-algo-bit.c
@@ -604,9 +604,10 @@ static int __i2c_bit_add_bus(struct i2c_adapter *adap,
                             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_adapter *adap,
        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)