On Mon, 15 Apr 2024 14:45:52 +0200 Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > On Sat, 2024-04-13 at 16:25 +0100, Jonathan Cameron wrote: > > On Fri, 12 Apr 2024 16:26:17 -0500 > > David Lechner <dlechner@xxxxxxxxxxxx> wrote: > > > > > On Thu, Apr 11, 2024 at 10:21 PM Kim Seer Paller > > > <kimseer.paller@xxxxxxxxxx> wrote: > > > > > > > > Define the sysfs interface for toggle capable channels. > > > > > > > > Toggle enabled channels will have: > > > > > > > > * out_voltageY_toggle_en > > The big missing thing in this ABI is a reference to existing precedence. > > You aren't actually defining anything new, it just hasn't yet been generalized > > beyond 1 device (unless you include PSK / FSK DDS drivers that are 'still' > > after > > 13+ years in staging!) > > > > This patch needs to be generalizing that documentation from the ltc2688. > > > > Probably in sysfs-bus-iio-dac > > > > > > > > It looks like there are 3 toggle modes. > > > > > > Two involve the notion of "enabled" outputs that I assume this attribute is > > > for: > > > > > > 1. Toggling all enabled pins at the same time using a software trigger > > > (global toggle bit) > > > 2. Toggling all enabled pins at the same time using a hardware trigger > > > (TGP pin) and toggling pins > > > > > > > This is presumably the tricky one as that hardware toggle may not be in > > control of the host CPU. > > > > > The third mode though looks like it uses the same toggle select > > > register for selecting A or B for each channel instead of enabling or > > > disabling each channel. > > > > > > 3. Toggling all pins to A or B based on the toggle select register. No > > > notion of enabled pins here. > > > > > > I haven't looked at the driver implementation, but it sounds like > > > out_voltageY_toggle_en and out_voltageY_symbol would be writing to the > > > same register in conflicting ways. So maybe we need yet another custom > > > attribute to select the currently active toggle mode? > > > > This one feels like it could be handled as a software optimisation over > > just changing the DAC value directly. > > Things may be slightly different in these devices. But for ltc2688 and AFAIR, > the symbol attribute is about toggling between A and B through SW (not really > enabling the mode). That interface will only pop up if there's no HW (PWM for > example) toggle present. I can't remember if we discussed it at the time of that driver, but from a userspace interface point of view, for a single channel there would be little point in this. I guess the key is it simultaneously switches a bunch of channels. Perhaps we can make that clearer in the ABI docs (if it isn't already clear enough!) So a software interface does seem appropriate. There is a fun question of whether the toggle select is useful to software. That is picking which of A or B each output uses for next toggle. At first glance I don't think so, but I'm open to people suggesting why that might need a userspace interface. Superficially feels like anything that can be done with that interface can also be done keeping all channels toggling to A or all to B at one time and potentially a few more register writes. Jonathan
