Re: Questions about IIO drivers

[Jonathan Cameron <jic23@cam.ac.uk>]

Hi Maxime,

> I'm currently writing a driver for the ADCs present in Atmel AT91 SoC
> using iio. I will of course submit it once it is ready.
> 
> For now, I have the basic integration into iio, and I am beginning to
> integrate the hardware logic in it. However, this integration raises few
> questions, and I didn't found any answers to it. (The dummy driver is of
> great help btw)
cool.  Any feedback on that particularly welcome given we haven't merged
it yet.
> 
>   - While the registers are all the same on the AT91 platform for the
> ADCs, the number of channels available is not the same from one board to
> another. For now, I'm declaring the number of channels available through
> the board definition and platform_data, and I'm declaring the channels
> to iio using :
> 
> 	idev->channels = kzalloc(sizeof(struct iio_chan_spec) * nb_chan,
> 				 GFP_KERNEL);
> 	for(i = 0; i < nb_chan; i++) {
> 		struct iio_chan_spec *chan = idev->channels + i;
> 		chan->type = IIO_IN;
> 		chan->indexed = 1;
> 		chan->channel = i;
> 	}
> 
> While it seems to work nicely, it generates a warning, as iio_dev's
> channels field is declared const. Is there a better solution ?

As an aside
IIO_IN -> IIO_VOLTAGE. I've push a patch to GregKH today that scraps
IIO_IN once and for all.

Are you using the latest published tree (currently on github)?
There's at least one driver that does the same in tree and it doesn't
give a warning (there were some core changes to avoid it).  ad7280a.

The other option is to have a single array of all channels and set
num_channels lower than the size of the array. Couple of drivers
do that for some of the parts they support.
> 
>   - For now, I don't really want to rely on hardware triggers, but
> instead use only software triggers. I've taken a look to sysfs triggers,
> and while the module for sysfs trigger is compiled and loaded, and added
> to the platform_devices of the board, the file trigger_now is nowhere to
> be found. I guess that I need to declare triggers in my driver, but I
> have found no clue on how to do that. How can we achieve it ?
Hmm.. clearly need some documentation for that driver.

What you should have is a directory called:
/sys/bus/iio/devices/iio_sysfs_trigger (it's a rather 'unusual device').

In there are the userspace controls for creating and destroying sysfs
triggers.

echo N to > add_trigger and you should find it has created a trigger
called sysfstrigN the controls for which (including the trigger_now) file
can be found in /sys/bus/iio/devices/triggerY (where Y is id of the
trigger - counting from 0).

Hope that helps,

Jonathan