On 22/11/15 12:08, Matt Ranostay wrote:
> On Sun, Nov 22, 2015 at 1:32 AM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>> On 18/11/15 01:49, Matt Ranostay wrote:
>>> Remove racey i2c_smbus_read_byte() calls in measurement
>>> reading function with an single i2c_transfer.
>>>
>>> Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx>
>> As with the lidar sensor, this requires a more sophisticated I2C master
>> so you should be checking if it is capable of doing what you need here.
>> Also, ideally provide a fallback to smbus for those cases where the
>> controller isn't sophisticated enough with appropriate locking to protect
>> the device...
>
> Ok should be simple enough. Is there an example of an iio driver doing
> this currently that I could use a reference?
Should be... (now I've got actually find one :)
adc/max1363 sort of does this - though in that case it only falls back to
smbus for 8 bit devices (IIRC the others perhaps can't be done as this
device clocks it's conversions of the i2c bus pulses)
Otherwise, grep is suggesting drivers simply fault out if what they want
isn't provided. Now there is some stuff to emulate bulk reads
in both i2c and regmap (recent so not necessarily in the iio tree yet).
However, I don't think it is relevant here.
This is one of those classic silly cases. If the driver had originally
been write to not support smbus only use, and checked for it then there
would have been no need to make it work. Now the driver does support it
we have a reason to continue to do so!
Jonathan
>
> Thanks,
>
> Matt
>
>>
>> Jonathan
>>> ---
>>> drivers/iio/chemical/vz89x.c | 33 +++++++++++++++++++++++----------
>>> 1 file changed, 23 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/iio/chemical/vz89x.c b/drivers/iio/chemical/vz89x.c
>>> index 11e59a5..c03f988 100644
>>> --- a/drivers/iio/chemical/vz89x.c
>>> +++ b/drivers/iio/chemical/vz89x.c
>>> @@ -100,27 +100,40 @@ static int vz89x_measurement_is_valid(struct vz89x_data *data)
>>> return !!(data->buffer[VZ89X_REG_MEASUREMENT_SIZE - 1] > 0);
>>> }
>>>
>>> +static int vz89x_i2c_xfer(struct vz89x_data *data, u8 cmd)
>>> +{
>>> + struct i2c_client *client = data->client;
>>> + struct i2c_msg msg[2];
>>> + int ret;
>>> + u8 buf[3] = { cmd, 0, 0};
>>> +
>>> + msg[0].addr = client->addr;
>>> + msg[0].flags = client->flags;
>>> + msg[0].len = 3;
>>> + msg[0].buf = (char *) &buf;
>>> +
>>> + msg[1].addr = client->addr;
>>> + msg[1].flags = client->flags | I2C_M_RD;
>>> + msg[1].len = VZ89X_REG_MEASUREMENT_SIZE;
>>> + msg[1].buf = (char *) &data->buffer;
>>> +
>>> + ret = i2c_transfer(client->adapter, msg, 2);
>>> +
>>> + return (ret == VZ89X_REG_MEASUREMENT_SIZE) ? 0 : ret;
>>> +}
>>> +
>>> static int vz89x_get_measurement(struct vz89x_data *data)
>>> {
>>> int ret;
>>> - int i;
>>>
>>> /* sensor can only be polled once a second max per datasheet */
>>> if (!time_after(jiffies, data->last_update + HZ))
>>> return 0;
>>>
>>> - ret = i2c_smbus_write_word_data(data->client,
>>> - VZ89X_REG_MEASUREMENT, 0);
>>> + ret = vz89x_i2c_xfer(data, VZ89X_REG_MEASUREMENT);
>>> if (ret < 0)
>>> return ret;
>>>
>>> - for (i = 0; i < VZ89X_REG_MEASUREMENT_SIZE; i++) {
>>> - ret = i2c_smbus_read_byte(data->client);
>>> - if (ret < 0)
>>> - return ret;
>>> - data->buffer[i] = ret;
>>> - }
>>> -
>>> ret = vz89x_measurement_is_valid(data);
>>> if (ret)
>>> return -EAGAIN;
>>>
>>
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