You need to understand how the pins are configured when defined in the devicetree. It is the driver that does the pin configuration as defined in the devicetree. Without an associated driver, the pins defined in the devicetree won’t do anything. When using PRU, there is no driver, so the pins don’t get configured and hence that is why pinmux-helper is necessary.
Regards, John > On Feb 28, 2017, at 9:32 PM, ags <alfred.g.schm...@gmail.com> wrote: > > If there is a better place for this post please move - after all, pinmux is > for more than GPIO, right? > > I've been trying to figure out why pinmux-helper is needed. I've searched and > found initial RFC and followup in the early years (by Charles Steinkuehler) > and I understand the motivation (I think) as stated, but I don't understand > the basics behind the why. > > Before pinmux-helper was provided, wasn't it possible to use sysfs to change > pinmux and gpio settings for all exported pins? Weren't all pins exported? > (If not, couldn't exporting them all have been an alternate solution?) And > couldn't loading a device tree fragment be used to change the current state? > If changes to pin state were to be made frequently, I can see how those > methods would be cumbersome; however, isn't pin state configuration something > that is done rather infrequently, as it implies that the BBB is being > repurposed and connected to different hardware (physically)? > > This question extends to config-pin utility, as well as the cape-universal > (and associated) dtb files. Wasn't all this possible already? > > Let me be clear that I'm not criticizing the work that has been done - rather > I'm trying to use the evolution of capes, cape manager, dtb, drivers etc as a > way of better understanding how the underlying drivers, device trees, and > sysfs controls work. > > -- > For more options, visit http://beagleboard.org/discuss > <http://beagleboard.org/discuss> > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com > <mailto:beagleboard+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/6ae54709-0f14-4a73-a01b-6efd024f4525%40googlegroups.com > > <https://groups.google.com/d/msgid/beagleboard/6ae54709-0f14-4a73-a01b-6efd024f4525%40googlegroups.com?utm_medium=email&utm_source=footer>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/E6A2E452-2FE6-426F-8975-467FACE5415E%40gmail.com. For more options, visit https://groups.google.com/d/optout.
