On Tue, 19 Jul 2022 15:27:24 +0200 Peter Rosin <peda@xxxxxxxxxx> wrote: > Hi! > > 2022-07-19 at 10:51, Jonathan Cameron wrote: > > On Mon, 18 Jul 2022 13:43:12 -0500 > > Chris Morgan <macroalpha82@xxxxxxxxx> wrote: > > > >> From: Chris Morgan <macromorgan@xxxxxxxxxxx> > >> > >> Copy the scan_type details from the parent iio channel to the child. > >> The scan_type is otherwise empty and things like the storagebits are > >> zero (which causes a problem for the adc-joystick driver which > >> validates the storagebits when used through a mux). I'm submitting this > >> as an RFC because I'm not sure if this is the correct way to handle > >> this scenario (a driver that checks the storagebits used with the iio > >> multiplexer). > >> > >> Signed-off-by: Chris Morgan <macromorgan@xxxxxxxxxxx> > > Seems sensible to me. Though Peter is expert on this one. > > I really doubt that it is this simple. I'm no expert on buffered channels, > but after a quick look it certainly looks like adc-joystick requires > buffered channels. And iio-multiplexer does not support that at all. I > think it could be supported, but in that case the only obvious support > would be to support buffered channels one at a time, and the way I > read adc-joystick it expects to get one sample for each axes in one > go (i.e. the way "normal" ADCs deliver multiple parallel samples). See > e.g. the call to iio_channel_get_all_cb in adc-joystick, which dives > right into the buffered iio department. > > So, the stuff in scan_type (along with scan_index, which is highly > related) is only relevant for buffered channels, and iio_multiplexer is > currently limited by its > > indio_dev->modes = INDIO_DIRECT_MODE; > > which is ... not buffered. :-( > > The simplest way forward is probably to lift the requirement of buffered > channels from adc-joystick, but that might be a hard sell as that driver > would then probably be a lot bigger and more complex. > Got it in one ;) There is a recent series from Chris adding polled support to adc_joystick (not yet merged) https://lore.kernel.org/all/20220705190354.69263-1-macromorgan@xxxxxxxxxxx/ That just reads the channels one at a time via same interfaces used for sysfs reads so would work with the iio-mux I think. Jonathan > That said, I would of course love to see the generic solution with support > for buffered channels in the mux, but my guess is that that gets much > more difficult, at least if you need the kind of buffered support > expected by adc-joystick. > > Or, am I misreading the whole situation and you have actually gotten it > to work with the below one-liner? If it works, fine by me, but I think > you also need to do something with scan_index? > > Cheers, > Peter > > > One comment on the comment inline... > >> --- > >> drivers/iio/multiplexer/iio-mux.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/drivers/iio/multiplexer/iio-mux.c b/drivers/iio/multiplexer/iio-mux.c > >> index 93558fddfa9b..1de01ec878c4 100644 > >> --- a/drivers/iio/multiplexer/iio-mux.c > >> +++ b/drivers/iio/multiplexer/iio-mux.c > >> @@ -322,6 +322,9 @@ static int mux_configure_channel(struct device *dev, struct mux *mux, > >> if (page) > >> devm_kfree(dev, page); > >> > >> + /* Copy scan type from parent to mux child. */ > > Comment is in the obvious category, so drop that. > > > >> + chan->scan_type = pchan->scan_type; > >> + > >> return 0; > >> } > >> > >
