2022-07-19 at 16:44, Chris Morgan wrote: > On Tue, Jul 19, 2022 at 03:19:01PM +0100, Jonathan Cameron wrote: >> 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 ;) I guess I'm old and can therefore allow myself to blather :-) >> There is a recent series from Chris adding polled support to adc_joystick (not yet merged) >> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20220705190354.69263-1-macromorgan%40hotmail.com%2F&data=05%7C01%7C%7Cfc07a056f5ae40ecc37908da6991a298%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637938371469723267%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=tAT8scZvG9Z8OVSgwdxog%2Bz55dzQC2TFddDa%2BQEX6e4%3D&reserved=0 >> 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 > > Right, correct that these two "work" together. Honestly the main thing > is that the adc-joystick driver checks for the storagebits, and that's > failing for me in this case when I use a mux. I added a one-liner to > the multiplexer code which added the parent information and that fixed > it. It's also possible that I could change the adc-joystick driver to > either not look for the storagebits or to change it to only look when > not doing polling mode. I just assumed that a missing scan_type was > an issue, so I added it and marked the patch as RFC because I wasn't > sure. If you want me to relax the adc-joystick check instead for polled > devices, I can. Ah, ok, there's been new development. Nice! As I said, I'm by no means a iio-buffer expert. On the contrary, I'm a total noob. So, be sure to take the following with a good pinch of salt, but I think that the adc-joystick driver in a mode that does not use iio-buffers should not then have artificial requirement on the buffer layout (scan_type). Don't forget the salt... :-) > Note that the adc-joystick driver does work perfectly fine with a mux, > I'm in the very early stages of upstreaming some devices which use it > in such a manner (the Anbernic RG353, Anbernic RG503, Odroid Go Super > are example devices that use the adc-joystick with a mux downstream). Cool! Cheers, Peter
