On Sun, Apr 12, 2015 at 8:59 AM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > 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). I agree. Although I think having some helper functions in IIO core should help keep the driver modifications to a minimum. >> >>> >>> 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. I agree we can't accurately synchronize the device frequency with the trigger frequency, but I think we can get it do a good enough level. I also see no difference in accuracy in doing it from userspace or from the driver itself. Why do you think it is a bad idea to synchronize the trigger sample frequency from the device sample frequency handler? I think that if we want to provide the hrtimer trigger from the driver itself, we should do this as well, otherwise there is no real gain to userspace. -- 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
