linux-kernel - Re: [PATCH 03/10] device property: Add fwnode_property_read_int

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Message-ID: <CAL_JsqLtRuzpQH=LnV45FFN=Gr_U403H2qfoPQskrCOknnwoyA@mail.gmail.com>
Date: Thu, 3 Apr 2025 12:22:59 -0500
From: Rob Herring <robh@...nel.org>
To: Remo Senekowitsch <remo@...nzli.dev>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Daniel Scally <djrscally@...il.com>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, Dirk Behme <dirk.behme@...bosch.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Saravana Kannan <saravanak@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	linux-acpi@...r.kernel.org, devicetree@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 03/10] device property: Add fwnode_property_read_int_array()

On Thu, Apr 3, 2025 at 12:04 PM Remo Senekowitsch <remo@...nzli.dev> wrote:
>
> On Thu Apr 3, 2025 at 6:08 PM CEST, Rob Herring wrote:
> > On Thu, Apr 3, 2025 at 8:29 AM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> >>
> >> On Wed, Apr 02, 2025 at 06:04:13PM +0200, Remo Senekowitsch wrote:
> >> > On Thu Mar 27, 2025 at 9:41 AM CET, Andy Shevchenko wrote:
> >> > > On Wed, Mar 26, 2025 at 06:13:42PM +0100, Remo Senekowitsch wrote:
> >> > >> The rust bindings for reading device properties has a single
> >> > >> implementation supporting differing sizes of integers. The fwnode C API
> >> > >> already has a similar interface, but it is not exposed with the
> >> > >> fwnode_property_ API. Add the fwnode_property_read_int_array() wrapper.
> >>
> >> ...
> >>
> >> > >> +EXPORT_SYMBOL_GPL(fwnode_property_read_int_array);
> >> > >
> >> > > I'm not sure about this. We have a lot of assumptions in the code that the
> >> > > arrays beneath are only represented by the selected number of integer types.
> >> > > This opens a Pandora's box, e.g., reading in u24, which is not supported by
> >> > > the upper layers..
> >> > >
> >> > >> +int fwnode_property_read_int_array(const struct fwnode_handle *fwnode, const char *propname,
> >> > >> +                             unsigned int elem_size, void *val, size_t nval);
> >> >
> >> > Here's an alternative approach using a macro to map each integer type explicitly
> >> > to its corresponding read function. There are some additional changes that will
> >> > be necessary to make the rest work, but this is the gist of it.
> >>
> >> I don;'t know Rust to tell anything about this, but at least it feels much
> >> better approach.
> >
> > I know a little Rust and it is much worse. It is implementing the same
> > code 8 times instead of 1 time just to work-around the C API.
>
> I prepared a functioning version of the macro-based approach. I'll post
> the patch for reference and discussion. We don't have to go with it.

Please wait for the discussion to finish.

Rob