Re: [PATCH 03/10] device property: Add fwnode_property_read_int_array()

Remo Senekowitsch
2025-04-04T12:30:07Z

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@linux.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.

Can you please elaborate on this concern?

The previous approach uses generics, which means the function is also
"copy-pasted" for each concrete type it is used with at compile time,
just like with a macro. So using a macro wouldn't be worse than generics
if binary size is the concern.

If the concern is about readability, I have managed to move all logic
outside the macro body, all that remains is the association between type
and `*_read_array` function.

Remo