V4L/DVB (5428): M920x: Detect zero-length I2C messages and fix a typo

Change a 00 to just 0
Detect zero-length I2C messages and return not supported.  I think I know
how to send one, but the problem is getting the slave's ack.  The only
point of a zero-length message is for probing; too see if the slave will
ack its address.  Since we don't know how to get the ack, we can't
support zero-length messages in a useful way, so it's probably best to
just return not supported for them.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/media/dvb/dvb-usb/m920x.c b/drivers/media/dvb/dvb-usb/m920x.c
index 08469ccabb72..8c954814f827 100644
--- a/drivers/media/dvb/dvb-usb/m920x.c
+++ b/drivers/media/dvb/dvb-usb/m920x.c
@@ -148,13 +148,18 @@ static int m9206_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
                 return -EAGAIN;
 
         for (i = 0; i < num; i++) {
-                if (msg[i].flags & (I2C_M_NO_RD_ACK|I2C_M_IGNORE_NAK|I2C_M_TEN)) {
+                if (msg[i].flags & (I2C_M_NO_RD_ACK|I2C_M_IGNORE_NAK|I2C_M_TEN) ||
+                    msg[i].len == 0) {
+                        /* For a 0 byte message, I think sending the address to index 0x80|0x40
+                         * would be the correct thing to do.  However, zero byte messages are
+                         * only used for probing, and since we don't know how to get the slave's
+                         * ack, we can't probe. */
                         ret = -ENOTSUPP;
                         goto unlock;
                 }
                 /* Send START & address/RW bit */
                 if (!(msg[i].flags & I2C_M_NOSTART)) {
-                        if ((ret = m9206_write(d->udev, M9206_I2C, (msg[i].addr<<1)|(msg[i].flags&I2C_M_RD?0x01:00), 0x80)) != 0)
+                        if ((ret = m9206_write(d->udev, M9206_I2C, (msg[i].addr<<1)|(msg[i].flags&I2C_M_RD?0x01:0), 0x80)) != 0)
                                 goto unlock;
                         /* Should check for ack here, if we knew how. */
                 }