linux-kernel - Re: [PATCH 1/2] device property: Add optional nargs_prop for get_reference

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Message-ID: <CAL_JsqL0tOahcAAqdT6n4q6b1OLwjmaDHfXgs=x4QGskQ2n+aw@mail.gmail.com>
Date: Tue, 8 Apr 2025 07:52:47 -0500
From: Rob Herring <robh@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Sean Anderson <sean.anderson@...ux.dev>, Saravana Kannan <saravanak@...gle.com>, 
	devicetree@...r.kernel.org, Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J . Wysocki" <rafael@...nel.org>, 
	Len Brown <lenb@...nel.org>, Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
	Daniel Scally <djrscally@...il.com>, linux-kernel@...r.kernel.org, 
	Danilo Krummrich <dakr@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/2] device property: Add optional nargs_prop for get_reference_args

On Tue, Apr 8, 2025 at 3:37 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Apr 07, 2025 at 06:37:13PM -0400, Sean Anderson wrote:
> > get_reference_args does not permit falling back to nargs when nargs_prop
> > is missing. This makes it difficult to support older devicetrees where
> > nargs_prop may not be present. Add support for this by converting nargs
> > to a signed value. Where before nargs was ignored if nargs_prop was
> > passed, now nargs is only ignored if it is strictly negative. When it is
> > positive, nargs represents the fallback cells to use if nargs_prop is
> > absent.
>
> And what is the case to support old DTs on most likely outdated hardware?

People still care when I break 1990s PowerMacs...

It's more that some bindings (like MSI) start out without #foo-cells,
and then we end up adding arg cells later. So we have to support no
#foo-cells means 0.

Rob