On Tue, May 20, 2008 at 01:28:17PM +0200, Jean Delvare wrote: > Hi Jonathan, > > On Tue, 20 May 2008 11:04:01 +0100, Jonathan Cameron wrote: > > This email is basically a request for opinions on how and where such sensors > > should be integrated into the kernel. > > > > To set the scene... > > > > Increasing numbers of embedded devices are being supplied attached MEMS > > devices (www.xbow.com imote2 etc). Along with more traditional sensors such > > as ADC's not being used for hardware monitoring, these do not really > > seem to > > fit with in an particular subsystem of the kernel. A previous > > discussion on > > lkml in 2006 considered the accelerometers to be found within some laptop > > hard drives, but I haven't been able to track down any more general > > discussions > > of such non hardware monitoring sensors. > > > > The obvious possibilities are: > > > > * To place the various drivers within the spi / i2c etc subsystems as > > relevant. > > Bad idea. Grouping drivers by connectivity is almost always the wrong > thing to do, as it means that different persons will maintain them and > they have all chances to diverge. You really want to group drivers by > functionality. On top of that, I am busy enough maintaining the i2c > core and bus drivers without having more i2c device drivers added to my > plate. These days I am trying to _empty_ drivers/i2c/chips, if anything. 100% ACK. And the functionality here is something like "industrial control" or "automation I/O". If this sort of hardware appears as device with mappable memory, we can handle it with UIO, but for SPI, I2C, USB, serial, we should have a new subsystem. It should handle not only input, but also similar output devices. It doesn't make sense to have ADCs in one subsystem, and DACs in a different one. > > > * To place within the hwmon subsystem as this is probably closest. > > (there is already at least one straight ADC driver in hwmon) > > Probably not the wisest choice, if nothing else, because the hwmon > maintainer is already overloaded. And I don't think that these devices > have much in common with the traditional hardware monitoring components > anyway. Agreed, hwmon devices are not really tuned for maximum performance, for example. Performance is often critical in automation control applications. > > I'm not sure what "straight ADC driver" you are referring to, but > anything which measures a voltage and exports the reading to user-space > is, well, a voltage sensor, and thus fix within hwmon. If the same chip > is used for a higher-level, dedicated function then we would probably > have a separate driver for it, outside of hwmon. > > > * To create a new subsystem, or perhaps merely sysfs class to contain these > > elements. > > Would be OK. Definitely. > Or: > > * Place these within the input subsystem. You might want to discuss > this with the input subsystem maintainer Dmitry Torokhov (Cc'd). The > Wii remote is essentially a joystick, and joysticks belong to the input > subsystem. This might apply to some devices, but not all. And the requirements are quite different, I think. > > This all sounds quite different from our hwmon drivers. Our hwmon > drivers read all the sensor values at once and cache the readings for a > couple seconds, so you can't get an instant reading at any time, and > they also don't support interrupts in general. Exactly. Thanks, Hans
