* Drew Fustini <drew@xxxxxxxxxxxxxxx> [200630 02:02]: > On Mon, Jun 29, 2020 at 10:03:58AM -0700, Tony Lindgren wrote: > > Hi, > > > > * Drew Fustini <drew@xxxxxxxxxxxxxxx> [200628 08:26]: > > > v2 changes: > > > - change default mux from output to input. Input is safer as it does > > > not drive the line. If the user wants output, they will need to edit > > > this device tree. > > > > So can you please clarify this a bit, are you saying that gpio output can't > > be done via userspace? > > As it stands, there is no way for userspace to change a pin from gpio > input to gpio output as it is based on the reciever active bit in the > pin control register (table 9-60 in the AM3358 datasheet [0]). OK. I guess one not so nice option would be to enable receiver active for all the gpio pins.. But this also affects power consumption a little. > I thought it would be useful to at least define the GPIOs available for > use on the PocketBeagle by default (and eventually the other BeagleBone > device trees). Input seems to be the safest value. This patch at least > makes it more clear where the user should edit to switch from input to > output. Some TI TRMs actually have tables listing the preferred mux logic for unused pins. I recall safe mode input pull down being one of the preferred modes. Sorry not sure which TRM that is, maybe omap3 or omap4 or omap5? > > Needing to change the dts does not sound good to me.. But maybe you mean > > this is needed until the gpio-omap and pinctrl-single patches are merged? > > I agree that I would like for userspace to be able to do run-time > changes. However, I think something would need to be added to the > pinconf support in pinctrl-single for that to be possible. There are > bias properties but non for receiver enable. > > Does it seem sensible to add that? Well let's see with Linus W says. To me it seems this might be a good reason to allow a sysfs interface to change the pinctrl if we don't have it yet? With the proper gpio line naming it should be quite simple to use too :) Regards, Tony
