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? -- 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
