V4L/DVB (5427): M920x: Improve I2C operations

Write some better documentation about what might be known about how the
m920x I2C works, since a datasheet is lacking.
The I2C xfer function should now handle more types of I2C transactions
than it could before.  Those it can't, will return error codes instead of
being executed incorrectly.  Multi-byte reads were not being done
correctly, which should be fixed.

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

1 files changed, 26 insertions, 26 deletions

diff --git a/drivers/media/dvb/dvb-usb/m920x.c b/drivers/media/dvb/dvb-usb/m920x.c
index 621819f6597a..08469ccabb72 100644
--- a/drivers/media/dvb/dvb-usb/m920x.c
+++ b/drivers/media/dvb/dvb-usb/m920x.c
@@ -141,43 +141,43 @@ static int m9206_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
         int i, j;
         int ret = 0;
 
+        if (!num)
+                return -EINVAL;
+
         if (mutex_lock_interruptible(&d->i2c_mutex) < 0)
                 return -EAGAIN;
 
         for (i = 0; i < num; i++) {
-                if (msg[i].flags & I2C_M_RD) {
-
-                        if ((ret = m9206_write(d->udev, M9206_I2C, (msg[i].addr << 1) | 0x01, 0x80)) != 0)
+                if (msg[i].flags & (I2C_M_NO_RD_ACK|I2C_M_IGNORE_NAK|I2C_M_TEN)) {
+                        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)
                                 goto unlock;
-
-                        for(j = 0; j < msg[i].len; j++) {
-                                if (j + 1 == msg[i].len && i + 1== num) {
-                                        if ((ret = m9206_read(d->udev, M9206_I2C, 0x0, 0x60, &msg[i].buf[j], msg[i].len)) != 0)
-                                                goto unlock;
-                                } else {
-                                        if ((ret = m9206_read(d->udev, M9206_I2C, 0x0, 0x21, &msg[i].buf[j], msg[i].len)) != 0)
-                                                goto unlock;
-                                }
+                        /* Should check for ack here, if we knew how. */
+                }
+                if (msg[i].flags & I2C_M_RD) {
+                        for (j = 0; j < msg[i].len; j++) {
+                                /* Last byte of transaction? Send STOP, otherwise send ACK. */
+                                int stop = (i+1 == num && j+1 == msg[i].len)?0x40:0x01;
+                                if ((ret = m9206_read(d->udev, M9206_I2C, 0x0, 0x20|stop, &msg[i].buf[j], 1)) != 0)
+                                        goto unlock;
                         }
-
                 } else {
-                        if ((ret = m9206_write(d->udev, M9206_I2C, msg[i].addr << 1, 0x80)) != 0)
-                                goto unlock;
-
-                        for(j = 0; j < msg[i].len; j++) {
-                                if (j + 1 == msg[i].len && i + 1== num) {
-                                        if ((ret = m9206_write(d->udev, M9206_I2C, msg[i].buf[j], 0x40)) != 0)
-                                                goto unlock;
-
-                                } else {
-                                        if ((ret = m9206_write(d->udev, M9206_I2C, msg[i].buf[j], 0x0)) != 0)
-                                                goto unlock;
-                                }
+                        for (j = 0; j < msg[i].len; j++) {
+                                /* Last byte of transaction? Then send STOP. */
+                                int stop = (i+1 == num && j+1 == msg[i].len)?0x40:0x00;
+                                if ((ret = m9206_write(d->udev, M9206_I2C, msg[i].buf[j], stop)) != 0)
+                                        goto unlock;
+                                /* Should check for ack here too. */
                         }
                 }
         }
         ret = num;
-        unlock:
+
+unlock:
         mutex_unlock(&d->i2c_mutex);
 
         return ret;