On 10/04/15 14:43, Daniel Baluta wrote: > 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! :) I'm actually beginning to have my doubts about whether my initial response here was right. Given your use cases and the complexity of matching frequencies, I think you are almost always better off implementing it in the drivers themselves (which can decide if there is new data or not). > >> >> 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. You can't that I can see. Hence you've convinced me this is a bad idea. > >> >> 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. I think this may well still be worth having, just not for your particular case. It would be useful for the devices that have a 'sample now' signal of some type that allows the trigger to control when they are sampling (and hence always match perfectly!) J > -- > 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 > -- 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
