Hans Verkuil wrote: >> Hi All, >> >> Nathan Lutchansky wrote: >> >>> At the moment, anyway. It will become more and more necessary as the >>> number of different I2C sensor chips on the market increases. V4L/DVB >>> has >>> already hit this problem in a big way. >>> >>> >>> >> DVB doesn't probe for i2c devices. The DVB adapter, ie the card knows >> what devices that are present and works under that assumption. >> >> Earlier DVB had the problem with probing. ie a different device is found >> at the expected location of another device(In the case of probing) and >> this device doesn't like to be fiddled around with. And "lo" we have a >> perfect freeze. >> >> After many such cases, DVB no longer probes for i2c devices (we now >> longer have anymore i2c issues) >> V4L on the other hand probes for all devices. This is IMHO wrong, due to >> >> (1) When the probe list grows long, it takes longer time for the probe >> to succeed (V4L guys themselves would agree to the fact that they have >> seen probes in the order of ~30 minutes ! Yuck) >> >> (2) Probing wrong devices >> >> So in any case probing can never be right, unless the card information >> is passed to the i2c core. But in that sense it is no longer a probe. It >> is indeed just an attach method. In that case, it makes no sense to make >> i2c core go around in circles. >> >> The proper way to handle this, is that only the right device is >> attached. Rather than making i2c to do this, subsystems should be >> handling this. >> > > OK, I'll repeat this one more time: for many of the older v4l cards we > have no idea on what addresses the i2c devices are. It was never > documented. And also some devices can move around depending on the card > revision (esp. true for the analog tuner). > That's no excuse to do things in a wrong way. Manu
