On Thu, Apr 9, 2015 at 8:18 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > On 08/04/15 14:30, Daniel Baluta wrote: >> On Mon, Apr 6, 2015 at 5:18 PM, Daniel Baluta <daniel.baluta@xxxxxxxxx> wrote: >>> This module is the core of IIO configfs. It creates the "iio" subsystem under >>> configfs mount point root, with one default group for "triggers". >>> >>> It offers basic interface for registering software trigger types. Next patches >>> will add "hrtimer" and "sysfs" trigger types. To add a new trigger type we must >>> create a new kernel module which implements iio_configfs_trigger.h interface. >>> >>> See Documentation/iio/iio_configfs.txt for more details on how configfs >>> support for IIO works. >>> >>> Signed-off-by: Daniel Baluta <daniel.baluta@xxxxxxxxx> >> >> Hi all, >> >> I also need your feedback on the following problem. >> >> We would like to be able to create hrtimer triggers from within >> a kernel module. There are cases where we don't have an interrupt >> pin or the interrupt pin is not connected, and we would like >> that applications to run unmodified with these types of sensors too. > A reasonable aim perhaps, as opposed to locally implemented polling > all over the place (which should definitely not happen). Yes, exactly! :) > > An alternative the zio guys used was to create timer > based triggers on the fly purely based on them being requested > (with an appropriate name IIRC)... Doesn't quite solve your > problem though as still needs userspace changes. >> >> We will split the current design into 3 parts: >> >> (1) IIO trigger handling generic part, which offers an API >> to register/unregister/get a reference to a trigger type >> >> (2) IIO configfs part that gets a reference to a trigger type and >> handles user requests to create/destroy a trigger. >> >> (3) IIO hrtimer driver that use the API at (1) for registering >> / deregistering a trigger type. >> >> Then, each driver in the case that it doesn't have a "real" trigger, >> will get a reference to a "hrtimer" trigger type and create >> a new "hrtimer" trigger. >> >> Does this look good to you? This could be easily done from >> userspace, but we will need to modify our userspace applications. > My initial thought is this really is a job for userspace, as should > be in most cases connecting up the device specific trigger as well > (as it's not always the right thing to use). > > In the general case it is far from obvious that an hrtimer is the > right option. Many usecases would be better off with a sysfs trigger > or even running off a different interrupt based trigger entirely. >> >> Also, handling sampling_frequency/delay would be transparent to >> applications if we provide this in kernel API. > Not really as sampling frequency in this case should only be an > attribute of the trigger, not the device. We only really allow > it for the device rather than always the triggers on the basis > that it has impacts on other device elements (events etc). Well, if the trigger is directly created from the driver then we will have a reference to a function that sets its delay. Each time the user sets the sampling frequency for the device with hit write_raw and there on IIO_CHAN_INFO_SAMP_FREQ case we also call set_delay(). Thus we always have have device sampling frequency in sync with trigger delay. I know this sounds crazy :) and I don't like it. I am not sure how to guarantee that device frequency is always in sync with trigger delay. > > Now sensible userspace ought to search for the trigger sysfs > directory and look there as well. > > I suppose if there is an awful lot of demand for this function > we could add a control knob somewhere that would set a 'default > trigger type' to be created for buffered devices that haven't > provided their own... I'm not overly keen though. >> This functionality would be very nice and useful, lets see if we can find some elegant way to do it. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
