linux-kernel - Re: [PATCH v1 2/2] of: property: Add device link support for pinctrl-0 through pinctrl-8

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Date:   Thu, 23 Jul 2020 07:29:12 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] of: property: Add device link support for
 pinctrl-0 through pinctrl-8

On Wed, Jul 22, 2020 at 7:08 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> On Wed, Jul 22, 2020 at 2:09 PM Rob Herring <robh+dt@...nel.org> wrote:
> >
> > On Wed, Jul 22, 2020 at 2:13 PM Saravana Kannan <saravanak@...gle.com> wrote:
> > >
> > > Add support for pinctrl-0 through pinctrl-8 explicitly instead of trying
> > > to add support for pinctrl-%d properties.
> > >
> > > Of all the pinctrl-* properties in dts files (20322), only 47% (9531)
> > > are pinctrl-%d properties. Of all the pinctrl-%d properties, 99.5%
> > > (9486) are made up of pinctrl-[0-2].
> > >
> > > Trying to parse all pinctrl-* properties and checking for pinctrl-%d is
> > > unnecessarily complicated. So, just add support for pinctrl-[0-8] for
> > > now. In the unlikely event we ever exceed pinctrl-8, we can come back
> > > and improve this.
> >
> > It wasn't immediately clear from this that pinctrl-8 is the current
> > max you found vs. a should be enough for a while.
>
> Hmmm... I tried. Looks like I failed. Open to copy-pasting any commit
> text that you think will make it clearer.

Append to the 2nd paragraph: 'pinctrl-8' is the current maximum found
in dts files.

> > Pinctrl is also a bit special in that we have 100s of child nodes and
> > only 1 to a few actual dependencies (the pinctrl node). I assume in
> > the end here, it's just the pin controller node that's the dependency
> > rather than creating lot's of dependencies?
>
> Correct. In the end, it just links to the one (or few) pin controller
> devices. Is there a requirement that all pinctrl-N properties point to
> the child state nodes of the same pin-controller node? Or can
> pinctrl-0 point to one and pinctrl-1 point to another pin controller
> node? If the former, all I'd need to do is parse pinctrl-0.

My initial thought was I'd expect the dependencies to be uniform
across pinctrl-%d properties as each one is supposed to be a different
mode of the same set of pins. However, the dra7 pathologic cases don't
follow that exactly with the higher speed MMC modes having an
additional i/o delay controller setting.

Rob