Hi, In trying to understand why my DVB USB tuner doesn't work with stock kernel drivers (4.2.0), I decided to pull out my logic analyser and sniff the I2C bus between the AF9035 and MXL5007T. I seem to have uncovered a couple of issues: 1) Attach fails because MXL5007T driver I2C soft reset fails. This is due to the preceding chip id read request that seems to hang the I2C bus and cause subsequent I2C commands to fail. 2) AF9035 driver I2C master xfer incorrectly implements "Write read" case. The FW expects register address fields to be used to send the I2C writes for register selection. The current implementation ignores these fields and the result is that only an I2C read is issued. Therefore the "0x3f" returned by the MXL5007T chip id query is not from the expected register. This is what is seen on the I2C bus: S | Read 0x60 + ACK | 0x3F + NAK | ... After which SDA is held low for ~6sec; reason for subsequent commands failing. 3) After modifying the AF9035 driver to fix point 2 and use the register address field, the following is seen on the I2C bus: S | Write 0x60 + ACK | 0xFB + ACK | 0xD9 + ACK | P S | Read 0x60 + ACK | 0x14 + NAK | ... This time we get an expected response, but the I2C bus still hangs with SDA held low and no Stop sequence. It seems that the MXL5007T is holding SDA low since the AF9035 happily cycles SCL trying to execute the subsequent writes. Without a solution to this, it seems that avoiding the I2C read is the best way to have the driver work correctly. There are no other tuner reads so point 2 above becomes moot for at least this device. Does anyone have any insight on the MXL5007T chip ID command and whether it should be issued in certain conditions? Any suggestions on how to resolve this given the above? Regards, Alessandro Radicati -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
