Commit 542134c0 authored Nov 21, 2017 by Eudean Sun Committed by Jiri Kosina Nov 21, 2017

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>

parent 20df1578

drivers/hid/hid-cp2112.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -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;

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