HID: cp2112: Fix I2C_BLOCK_DATA transactions

The existing driver erroneously treats I2C_BLOCK_DATA and BLOCK_DATA
commands the same.

For I2C_BLOCK_DATA reads, the length of the read is provided in
data->block[0], but the length itself should not be sent to the slave. In
contrast, for BLOCK_DATA reads no length is specified since the length
will be the first byte returned from the slave. When copying data back
to the data buffer, for an I2C_BLOCK_DATA read we have to take care not to
overwrite data->block[0] to avoid overwriting the length. A BLOCK_DATA
read doesn't have this concern since the first byte returned by the device
is the length and belongs in data->block[0].

For I2C_BLOCK_DATA writes, the length is also provided in data->block[0],
but the length itself is not sent to the slave (in contrast to BLOCK_DATA
writes where the length prefixes the data sent to the slave).

This was tested on physical hardware using i2cdump with the i and s flags
to test the behavior of I2C_BLOCK_DATA reads and BLOCK_DATA reads,
respectively. Writes were not tested but the I2C_BLOCK_DATA write change
is pretty simple to verify by inspection.

Signed-off-by: Eudean Sun <eudean@arista.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
index 68cdc962265b..271f31461da4 100644
--- a/drivers/hid/hid-cp2112.c
+++ b/drivers/hid/hid-cp2112.c
@@ -696,8 +696,16 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
                                               (u8 *)&word, 2);
                 break;
         case I2C_SMBUS_I2C_BLOCK_DATA:
-                size = I2C_SMBUS_BLOCK_DATA;
-                /* fallthrough */
+                if (read_write == I2C_SMBUS_READ) {
+                        read_length = data->block[0];
+                        count = cp2112_write_read_req(buf, addr, read_length,
+                                                      command, NULL, 0);
+                } else {
+                        count = cp2112_write_req(buf, addr, command,
+                                                 data->block + 1,
+                                                 data->block[0]);
+                }
+                break;
         case I2C_SMBUS_BLOCK_DATA:
                 if (I2C_SMBUS_READ == read_write) {
                         count = cp2112_write_read_req(buf, addr,
@@ -785,6 +793,9 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
         case I2C_SMBUS_WORD_DATA:
                 data->word = le16_to_cpup((__le16 *)buf);
                 break;
+        case I2C_SMBUS_I2C_BLOCK_DATA:
+                memcpy(data->block + 1, buf, read_length);
+                break;
         case I2C_SMBUS_BLOCK_DATA:
                 if (read_length > I2C_SMBUS_BLOCK_MAX) {
                         ret = -EPROTO;