On Mon, Jul 7, 2014 at 9:57 PM, Benjamin Tissoires
[off-list ref] wrote:

Hi Antonio,

On Sun, Jun 29, 2014 at 2:14 AM, Antonio Borneo
[off-list ref] wrote:

quoted

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

quoted

Signed-off-by: Antonio Borneo <redacted>
---
 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.

quoted

+               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;

quoted

+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

quoted

+}
+
 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