Re: [PATCH] HID: cp2112: add I2C mode

[Antonio Borneo]

On Mon, Jul 7, 2014 at 9:57 PM, Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxx> wrote:
> Hi Antonio,
>
> On Sun, Jun 29, 2014 at 2:14 AM, Antonio Borneo
> <borneo.antonio@xxxxxxxxx> wrote:
>> cp2112 supports single I2C read/write transactions.
>> It can't combine I2C transactions.
>>
>> Add master_xfer, using similar code flow as for smbus_xfer.
>
> Thanks for taking the time to implement it. I wanted to add this
> functionality, but did not found the time to finalize/submit the
> patches.
> So here is a review.

Ciao Benjamin,

thanks for the review.
My comments inline below

>>
>> Signed-off-by: Antonio Borneo <borneo.antonio@xxxxxxxxx>
>> ---
>>  drivers/hid/hid-cp2112.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 101 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
>> index 3952d90..1260a8a 100644
>> --- a/drivers/hid/hid-cp2112.c
>> +++ b/drivers/hid/hid-cp2112.c
>> @@ -429,6 +429,104 @@ static int cp2112_write_req(void *buf, u8 slave_address, u8 command, u8 *data,
>>         return data_length + 4;
>>  }
>>
>> +static int cp2112_i2c_write_req(void *buf, u8 slave_address, u8 *data,
>> +                               u8 data_length)
>> +{
>> +       struct cp2112_write_req_report *report = buf;
>> +
>> +       if (data_length > sizeof(report->data))
>> +               return -EINVAL;
>> +
>> +       report->report = CP2112_DATA_WRITE_REQUEST;
>> +       report->slave_address = slave_address << 1;
>> +       report->length = data_length;
>> +       memcpy(report->data, data, data_length);
>> +       return data_length + 3;
>> +}
>> +
>> +static int cp2112_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>> +                          int num)
>> +{
>> +       struct cp2112_device *dev = (struct cp2112_device *)adap->algo_data;
>> +       struct hid_device *hdev = dev->hdev;
>> +       u8 buf[64];
>> +       ssize_t count;
>> +       unsigned int retries;
>> +       int ret;
>> +
>> +       hid_dbg(hdev, "I2C %d messages\n", num);
>> +
>> +       if (num != 1) {
>> +               hid_err(hdev,
>> +                       "Multi-message I2C transactions not supported\n");
>
> This is a shame. You can just externalize the following block (in pseudo code):
> { - read/write_req
>   - hid_output
>   - xfer_status
>   - read}
>
> and then just use a for loop to call this sequence for each incoming message.

The parameter "num" is for sending a "combined I2C transaction" in which
a series of messages is sent "without" stop-bits between the messages.
You can get full description searching for "i2c_transfer" in
  - Documentation/i2c/writing-clients
  - Documentation/i2c/i2c-protocol
Since CP2112 does not support this feature, I return EOPNOTSUPP as is done in
  drivers/i2c/busses/i2c-powermac.c

If I implement the loop, as you suggest, CP2112 will just send a
sequence of independent messages, each with its own stop bit.

Probably the error message could be more explicit by mentioning the
word "combined".
I lazily copied the same message from i2c-powermac think it's clear enough.

>
>> +               return -EOPNOTSUPP;
>> +       }
>> +
>> +       if (msgs->flags & I2C_M_RD)
>> +               count = cp2112_read_req(buf, msgs->addr, msgs->len);
>> +       else
>> +               count = cp2112_i2c_write_req(buf, msgs->addr, msgs->buf,
>> +                                            msgs->len);
>> +
>> +       if (count < 0)
>> +               return count;
>> +
>> +       ret = hid_hw_power(hdev, PM_HINT_FULLON);
>> +       if (ret < 0) {
>> +               hid_err(hdev, "power management error: %d\n", ret);
>> +               return ret;
>> +       }
>> +
>> +       ret = cp2112_hid_output(hdev, buf, count, HID_OUTPUT_REPORT);
>> +       if (ret < 0) {
>> +               hid_warn(hdev, "Error starting transaction: %d\n", ret);
>> +               goto power_normal;
>> +       }
>> +
>> +       for (retries = 0; retries < XFER_STATUS_RETRIES; ++retries) {
>> +               ret = cp2112_xfer_status(dev);
>> +               if (-EBUSY == ret)
>> +                       continue;
>> +               if (ret < 0)
>> +                       goto power_normal;
>> +               break;
>> +       }
>> +
>> +       if (XFER_STATUS_RETRIES <= retries) {
>> +               hid_warn(hdev, "Transfer timed out, cancelling.\n");
>> +               buf[0] = CP2112_CANCEL_TRANSFER;
>> +               buf[1] = 0x01;
>> +
>> +               ret = cp2112_hid_output(hdev, buf, 2, HID_OUTPUT_REPORT);
>> +               if (ret < 0)
>> +                       hid_warn(hdev, "Error cancelling transaction: %d\n",
>> +                                ret);
>> +
>> +               ret = -ETIMEDOUT;
>> +               goto power_normal;
>> +       }
>> +
>> +       if (!(msgs->flags & I2C_M_RD)) {
>> +               ret = 0;
>> +               goto power_normal;
>> +       }
>> +
>> +       ret = cp2112_read(dev, msgs->buf, msgs->len);
>> +       if (ret < 0)
>> +               goto power_normal;
>> +       if (ret != msgs->len) {
>> +               hid_warn(hdev, "short read: %d < %d\n", ret, msgs->len);
>> +               ret = -EIO;
>> +               goto power_normal;
>> +       }
>> +
>> +       ret = 0;
>
> ret = num;
>
>> +power_normal:
>> +       hid_hw_power(hdev, PM_HINT_NORMAL);
>> +       hid_dbg(hdev, "I2C transfer finished: %d\n", ret);
>> +       return (ret) ? ret : 1;
>
> and "return ret;"

Not sure I catch what you mean, here. Please confirm my understanding.

>From a comment inside include/linux/i2c.h
        /* master_xfer should return the number of messages successfully
           processed, or a negative value on error */

In the code above I set "ret" to an error number or to zero.
Then return the error number or the number of messages (equal to 1, as
explained above).

Do you prefer I set "ret" directly to 1 instead of 0?

I can send a V2 for this.
In this case I would not change the debug message above that prints
"ret" and I will just print the current value for "ret".

Best Regards,
Antonio

>
>> +}
>> +
>>  static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
>>                        unsigned short flags, char read_write, u8 command,
>>                        int size, union i2c_smbus_data *data)
>> @@ -595,7 +693,8 @@ power_normal:
>>
>>  static u32 cp2112_functionality(struct i2c_adapter *adap)
>>  {
>> -       return I2C_FUNC_SMBUS_BYTE |
>> +       return I2C_FUNC_I2C |
>> +               I2C_FUNC_SMBUS_BYTE |
>>                 I2C_FUNC_SMBUS_BYTE_DATA |
>>                 I2C_FUNC_SMBUS_WORD_DATA |
>>                 I2C_FUNC_SMBUS_BLOCK_DATA |
>> @@ -605,6 +704,7 @@ static u32 cp2112_functionality(struct i2c_adapter *adap)
>>  }
>>
>>  static const struct i2c_algorithm smbus_algorithm = {
>> +       .master_xfer    = cp2112_i2c_xfer,
>>         .smbus_xfer     = cp2112_xfer,
>>         .functionality  = cp2112_functionality,
>>  };
>> --
>> 2.0.1
>>
>
> Cheers,
> Benjamin
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