On Mon, 7 Feb 2022 15:38:40 +0100 Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote: > As part of a previous discussion with Jonathan Cameron [1], it appeared > necessary to clarify the meaning of each mode so that new developers > could understand better what they should use or not use and when. > > The idea of renaming these modes as been let aside because naming is a > big deal and requires a lot of thinking. So for now let's focus on > correctly explaining what each mode implies. > > [1] https://lore.kernel.org/linux-iio/20210930165510.2295e6c4@jic23-huawei/ > > Suggested-by: Jonathan Cameron <jic23@xxxxxxxxxx> > Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx> One trivial thing inline as a result of edits in v3. Otherwise, I want to let this series sit a little longer and ideally get some eyes on the st_sensors patches. Jonathan > --- > include/linux/iio/iio.h | 49 ++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 48 insertions(+), 1 deletion(-) > > diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h > index 85cb924debd9..e383b0d96035 100644 > --- a/include/linux/iio/iio.h > +++ b/include/linux/iio/iio.h > @@ -315,7 +315,54 @@ static inline bool iio_channel_has_available(const struct iio_chan_spec *chan, > s64 iio_get_time_ns(const struct iio_dev *indio_dev); > unsigned int iio_get_time_res(const struct iio_dev *indio_dev); > > -/* Device operating modes */ > +/** > + * Device operating modes > + * @INDIO_DIRECT_MODE: There is an access to either: > + * a) The last single value available for devices that do not provide > + * on-demand reads. > + * b) A new value after performing an on-demand read otherwise. > + * On most devices, this is a single-shot read. On some devices with data > + * streams without an 'on-demand' function, this might also be the 'last value' > + * feature. This block duplicates what you now have as a/b above. I can drop it whilst applying if nothing else comes up. > Above all, this mode internally means that we are not in any of the > + * other modes, and sysfs reads should work. > + * Device drivers should inform the core if they support this mode. > + * @INDIO_BUFFER_TRIGGERED: Common mode when dealing with kfifo buffers. > + * It indicates that an explicit trigger is required. This requests the core to > + * attach a poll function when enabling the buffer, which is indicated by the > + * _TRIGGERED suffix. > + * The core will ensure this mode is set when registering a triggered buffer > + * with iio_triggered_buffer_setup(). > + * @INDIO_BUFFER_SOFTWARE: Another kfifo buffer mode, but not event triggered. > + * No poll function can be attached because there is no triggered infrastructure > + * we can use to cause capture. There is a kfifo that the driver will fill, but > + * not "only one scan at a time". Typically, hardware will have a buffer that > + * can hold multiple scans. Software may read one or more scans at a single time > + * and push the available data to a Kfifo. This means the core will not attach > + * any poll function when enabling the buffer. > + * The core will ensure this mode is set when registering a simple kfifo buffer > + * with devm_iio_kfifo_buffer_setup(). > + * @INDIO_BUFFER_HARDWARE: For specific hardware, if unsure do not use this mode. > + * Same as above but this time the buffer is not a kfifo where we have direct > + * access to the data. Instead, the consumer driver must access the data through > + * non software visible channels (or DMA when there is no demux possible in > + * software) > + * The core will ensure this mode is set when registering a dmaengine buffer > + * with devm_iio_dmaengine_buffer_setup(). > + * @INDIO_EVENT_TRIGGERED: Very unusual mode. > + * Triggers usually refer to an external event which will start data capture. > + * Here it is kind of the opposite as, a particular state of the data might > + * produce an event which can be considered as an event. We don't necessarily > + * have access to the data itself, but to the event produced. For example, this > + * can be a threshold detector. The internal path of this mode is very close to > + * the INDIO_BUFFER_TRIGGERED mode. > + * The core will ensure this mode is set when registering a triggered event. > + * @INDIO_HARDWARE_TRIGGERED: Very unusual mode. > + * Here, triggers can result in data capture and can be routed to multiple > + * hardware components, which make them close to regular triggers in the way > + * they must be managed by the core, but without the entire interrupts/poll > + * functions burden. Interrupts are irrelevant as the data flow is hardware > + * mediated and distributed. > + */ > #define INDIO_DIRECT_MODE 0x01 > #define INDIO_BUFFER_TRIGGERED 0x02 > #define INDIO_BUFFER_SOFTWARE 0x04
