Re: [spi-devel-general] Accelerometer, Gyros and ADC's etc within the kernel.

[Ben Dooks <ben@fluff.org>]

On Tue, May 27, 2008 at 08:44:15PM +0400, Anton Vorontsov wrote:
> Hi Jonathan,
> 
> On Tue, May 20, 2008 at 11:04:01AM +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.
> > 
> > * To place within the hwmon subsystem as this is probably closest.
> > (there is already at least one straight ADC driver in hwmon)
> > 
> > * To create a new subsystem, or perhaps merely sysfs class to contain these
> >   elements.
> > 
> > Typical requirements within an application include simply polling for 
> > current
> > readings, and using device triggered interrupts to grab data 
> > continuously to a
> > ring buffer, for collection by suitable userspace code.  Obviously it 
> > would be
> > desirable to standardize sysfs controls for various calibration 
> > parameters as
> > much as possible across the various devices.

The two drivers i've seen so far use the input subsystem to report
their data to the user. I'm working on an driver for the SMB380 which
can be both i2c and spi.
 
> Also, I'd mention that most ADC devices could report in "bunched" mode,
> i.e.
> 
> 1. Request ADC readings from pins X, Y, Z1, Z2.
> 2. Wait for single IRQ
> 3. Read all the results
> 
> At handhelds.org, we've wrote quite good (I think) ADC subsystem,
> that keeps in mind ADC capabilities. It implements two interfaces:
> in-kernel (e.g. for touchscreen drivers), and userspace interface via
> sysfs. I was planning to implement drivers/input/ interface too.

handhelds.org's track history of getting things into the kernel
is poor.

-- 
-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.