On Tue, Nov 4, 2014 at 10:27 AM, Bastien Nocera <hadess@xxxxxxxxxx> wrote: > On Tue, 2014-11-04 at 10:18 +0200, Daniel Baluta wrote: >> On Tue, Nov 4, 2014 at 1:01 AM, Bastien Nocera <hadess@xxxxxxxxxx> wrote: >> > On Wed, 2014-10-29 at 19:30 +0100, Lars-Peter Clausen wrote: >> >> On 10/29/2014 06:47 PM, Bastien Nocera wrote: >> >> > On Wed, 2014-10-29 at 18:39 +0100, Lars-Peter Clausen wrote: >> >> >> On 10/29/2014 06:33 PM, Bastien Nocera wrote: >> >> >>> On Wed, 2014-10-29 at 18:21 +0100, Lars-Peter Clausen wrote: >> >> >>>> On 10/29/2014 03:30 PM, Bastien Nocera wrote: >> >> >>>>> Hey, >> >> >>>>> >> >> >>>>> I've posted this a couple of days ago: >> >> >>>>> http://www.hadess.net/2014/10/a-gnome-kernel-wishlist.html >> >> >>>>> along with a mail to LKML: >> >> >>>>> http://thread.gmane.org/gmane.linux.kernel/1810083 >> >> >>>>> >> >> >>>>> I've recently added to my list an item about IIO: >> >> >>>>> https://wiki.gnome.org/BastienNocera/KernelWishlist >> >> >>>>> >> >> >>>>> Are there any plans for a better API for the IIO subsystem? The API >> >> >>>>> might be good enough to drive from shell scripts, or helpers that only >> >> >>>>> need to work with one variant of a device, but my attempts at trying to >> >> >>>>> use the IIO subsystem to provide an accelerometer to do automatic >> >> >>>>> display rotation[1] showed that the API is really cumbersome. >> >> >>>>> >> >> >>>>> The code I wrote spends most of its time creating sysfs paths, reading >> >> >>>>> values in different formats, and mangling filenames[2]. >> >> >>>>> >> >> >>>>> Is an ioctl-based API planned? Something where I could get/set >> >> >>>>> structures to gather metadata about the device, and set it up easily, so >> >> >>>>> reading data from it is easier? >> >> >>>> >> >> >>>> No, unfortunately not and I'm not sure if such a ABI would be accepted if >> >> >>>> proposed. >> >> >>> >> >> >>> Why not? >> >> >> >> >> >> Because it means there will be ambiguity in the API on how to do things. >> >> >> Which is typically not a desired property. >> >> >> >> >> >>> >> >> >>>> But checkout libiio[1][2], it hides the details of the sysfs file manipulation. >> >> >>> >> >> >>> I'm not sure that's any better unfortunately. I've certainly tried to do >> >> >>> that already in my code, but that doesn't change that the user-space API >> >> >>> is barely usable. >> >> >> >> >> >> It's not completely unusable ;) >> >> > >> >> > In the end, you prefer the "self-documenting" of using sysfs files, >> >> > rather than an API which you can document in a header file? >> >> >> >> If it was for me we'd be using a state-full IOCTL ABI rather than a >> >> stateless sysfs ABI. I'm definitely not happy with the current interface, >> >> but it's the interface we have. But the problem with userspace ABI (in >> >> comparison to in-kernel API) is that we can just change things at random, >> >> but we have to stick with the existing interface. >> >> >> >> The sysfs ABI is not meant to be self documenting and it is not >> >> undocumented. The documentation for the different attributes can be found in >> >> Documentation/ABI/testing/sysfs-bus-iio[1]. >> > >> > That's useful if a bit terse. Thanks though. >> > >> >> > I don't understand that. My questions on this very mailing-list, and >> >> > comments that were made to users of my code[1] clearly show that the >> >> > existing API is anything but "not ambiguous". >> >> >> >> That bug report sounds like bugs in the driver. >> > >> > Not really. Some drivers need the "in_accel_hysteresis" set, some don't >> > have that sysfs file, for example. >> > >> >> > I've used the Bluetooth, input, rfkill, and inotify APIs as provided >> >> > directly by the Linux kernel (not through a layer) and they're of better >> >> > quality than the IIO one. >> >> > >> >> > I just don't see how one could support a class of IIO sensors with the >> >> > existing API. >> >> >> >> I can understand your frustration. A API that is not usable in a generic way >> >> is not really useful. So we should try to fix that, but we are bound by the >> >> framework itself and can't just throw everything away. >> >> >> >> So lets start by trying to identify what is missing. Which information do >> >> you think could be provided by using a IOCTL interface which you need or >> >> want which is not provided by the current sysfs interface or can not be >> >> provided by the current sysfs interface. >> > >> > (pseudo code ahead) >> > >> > First, being able to cut down on the string manipulation would be great. >> > So instead of doing: >> > accel_x_path = build_filename (sysfs_path, "in_accel_x_raw"); >> > accel_y_path = build_filename (sysfs_path, "in_accel_y_raw"); >> > accel_z_path = build_filename (sysfs_path, "in_accel_z_raw"); >> > if (exists(accel_x_path) && exists(accel_y_path) && exists(accel_z_path)) { >> > // We have an accelerometer >> > do_something(); >> > } >> > free(..x); >> > free(..y); >> > free(..z); >> > free(sysfs_path); >> > >> > I could query for the device's capabilities: >> > fd = open ("/dev/iio0"); >> > ioctl(fd, IIO_GET_CAPS, &caps); >> > if (caps.channels & (IIO_CAP_ACCEL_X | IIO_CAP_ACCEL_Y | IIO_CAP_ACCEL_Z)) { >> > // We have an accelerometer >> > do_something(); >> > } >> > >> > Note that, from the data given, I don't know how to make out whether >> > something is an accelerometer, or a quartenion sensor, or which one we >> > should prefer on specific machines. >> > >> > This would also be stateful, so that 1) enabling the various channels, >> > 2) changing the hysteresis would be reset when the fd is closed. That >> > would cut down on the power consumption when unused, or when the service >> > that uses that data crashes. >> > >> > Finally, there's some documentation, and it's not quite finished, or >> > there's something fishy on this device: >> > $ ls /sys//devices/platform/80860F41:04/i2c-12/i2c-SMO8500:00/iio:device0/events >> > in_accel_x_thresh_thresh_en in_accel_x_thresh_thresh_value >> > in_accel_y_thresh_thresh_period in_accel_z_thresh_thresh_en >> > in_accel_z_thresh_thresh_value >> > in_accel_x_thresh_thresh_period in_accel_y_thresh_thresh_en >> > in_accel_y_thresh_thresh_value in_accel_z_thresh_thresh_period >> >> Could you paste here the initialization part of iio_chan_spec + iio_event_spec? > > How would I do that? Just look into the code and search for iio_chan_spec and iio_event_spec declaration. e.g: For iio_chan_spec: static const struct iio_chan_spec iio_dummy_channels[] = { » { » » .type = IIO_VOLTAGE, » » .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), » » .output = 1, » » .indexed = 1, » » .channel = 0, » }, }; For iio_event_spec: static const struct iio_event_spec iio_dummy_event = { » .type = IIO_EV_TYPE_THRESH, » .dir = IIO_EV_DIR_RISING, » .mask_separate = BIT(IIO_EV_INFO_VALUE) | BIT(IIO_EV_INFO_ENABLE), }; -- 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
