Linux-OMAP Archive on
 help / color / Atom feed
From: Tony Lindgren <>
To: Drew Fustini <>
Cc: Rob Herring <>,,,,,
	Jason Kridner <>,
	Robert Nelson <>,
	"H . Nikolaus Schaller" <>,
	Linus Walleij <>
Subject: Re: [PATCH v2] ARM: dts: am335x-pocketbeagle: set default mux for gpio pins
Date: Tue, 30 Jun 2020 11:20:37 -0700
Message-ID: <> (raw)
In-Reply-To: <20200630020102.GA45128@x1>

* Drew Fustini <> [200630 02:02]:
> On Mon, Jun 29, 2020 at 10:03:58AM -0700, Tony Lindgren wrote:
> > Hi,
> > 
> > * Drew Fustini <> [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 :)



  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-28 15:24 Drew Fustini
2020-06-29 17:03 ` Tony Lindgren
2020-06-30  2:01   ` Drew Fustini
2020-06-30 18:20     ` Tony Lindgren [this message]
2020-06-30 21:31       ` Drew Fustini
2020-06-30 21:34         ` Tony Lindgren
2020-06-30 21:42           ` Drew Fustini
2020-07-01 14:48             ` Tony Lindgren

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-OMAP Archive on

Archives are clonable:
	git clone --mirror linux-omap/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-omap linux-omap/ \
	public-inbox-index linux-omap

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone