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From:   Saravana Kannan <saravanak@google.com>
Date:   Wed, 22 Jul 2020 18:01:57 -0700
Message-ID: <CAGETcx-CajYnh=ZOkGBxrSUHe0uTAwJ_gZ8EJV1jrq-jNmaBVw@mail.gmail.com>
Subject: Re: [PATCH v1 2/2] of: property: Add device link support for
 pinctrl-0 through pinctrl-8
To:     Frank Rowand <frowand.list@gmail.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Wed, Jul 22, 2020 at 1:56 PM Frank Rowand <frowand.list@gmail.com> wrote:
>
> On 2020-07-22 15:13, Saravana Kannan 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.
>
> If you were to implement the more general pinctrl-* case, roughly what would
> it look like (pseudo-code or english description is fine).

So when I say "unnecessarily complicated", it's in terms of
readability. I can't use these macros -- which are succinct 1 line
entries that are super easy to understand.

Pseudo code:
parse_pinctrl(np, prop_name, index)
{
    if (doens't start with "pinctrl-")
        return NULL;
    ret = kstrtouint(propname + strlen("pinctrl"), 10, &val);

    check that it's not something line "pinctrl-2nd-val" that'll still
set val to 2.

    parse phandle with args and return phandle node.
}

All this when effectively 99.5% of the DT just use pinctrl-0,
pinctrl-1 and pinctrl-2. There are a few that use pinctrl-3. And
literally 6 DT files in the entire kernel source tree use pinctrl-4 or
greater.

And for those 6 files, pinctrl-[0-8] really point to the same pinctrl
node. So even if I didn't parse pinctrl-[4-8], all the device
dependencies would be tracked properly.

-Saravana