On Thu, 4 Feb 2021 13:35:49 +0200 <alexandru.tach...@analog.com> wrote:
> From: Alexandru Tachici <alexandru.tach...@analog.com> > > AD7124-8 can have up to 16 pseudo-differential channels > enabled simultaneously and only 8 configurations. I'm curious. Datasheet says up to 15 pseudo differential channels. I can't immediate see why though! > In this > scenario we cannot assign one configuration per channel, > some channels will have to share configurations like, ODR, > gain and filter parameters. > > Allow the user to specify channels and configurations > separately in device-tree and assign, if needed, the same > configuration to multiple channels. > > If two channels share the configuration changing the > sampling rate of one will change the sampling rate of the > other too. I can see why you want to do this via device tree to keep things simple, but it does sort of feel like it might be something we 'should' be configuring from userspace. This is unlike the whether the channels should be differential or not in the first place (which is mostly down to what they are wired up to). It's a little bit of a mess as some things like the reference are in the 8 config registers and we already have those in the per channel description. I'm trying to get my head around how we might do this in the ideal case. So what we'd want would be: 1) Userspace to not have to care about this restriction if whatever it requests is 'possible'. 2) If multiple channels have the same config, then we'd want to 'pack' them into the same configuration register. 3) Be as flexible as possible. The problem is we don't have any way in the ABI of making atomic adjustments to multiple parameters, but perhaps it 'could' be made to work as follows. 1) All settings go through a level of indirection - i.e. we cache them in the driver and only apply them as needed. 2) Sysfs raw reads work on a basis of LRU + packing where we can. (or we just use one config and pay the cost of switching every time) 3) Buffered reads. We check whether the requested configuration of all channels is possible and set it up if so. Otherwise we return -EBUSY or similar to indicate that what is currently requested can't be done. Hence we make it atomic at the point of enable. Most of the time, I'm going to assume that users either have a carefully crafted optimum setup for their system in which case they can read the datasheet to figure out what is possible or they want to have a small number of groups of channels where it makes sense to replicate configuration because they are reading the 'same sort of thing'. Perhaps just pushing all this to dt is fine, but I'm not that keep on it if there is a reasonable way to avoid it. Things like filter selections and calibration offsets shouldn't be influenced by DT (by putting them in shared groups like this series does). These are weirdly flexible devices (what fun!) :) Jonathan > > Alexandru Tachici (2): > iio: adc: ad7124: allow 16 channels > dt-bindings: iio: adc: ad7124: add config nodes > > .../bindings/iio/adc/adi,ad7124.yaml | 72 +++++-- > drivers/iio/adc/ad7124.c | 183 +++++++++++------- > 2 files changed, 166 insertions(+), 89 deletions(-) >
