On 15/04/15 21:58, Octavian Purdila wrote: > 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. > You will get beating problems. So once in a while you'll either miss a reading or you'll get a bonus one. The point about doing it in the driver is that you actually poll at a higher frequency, but only fire a trigger if there is something there (by reading the dataready register or equivalent). Thus your trigger acts more or less the same as a wired interrupt. You can't do this with an external hrtimer trigger. 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
