[PATCH RFC 02/11] ACPI: Introduce irq_get() for static fwnodes

[Jonathan Cameron]

On Mon, 28 Sep 2026 18:15:37 +0200
Lorenzo Pieralisi <lpieralisi at kernel.org> wrote:

> On Fri, Sep 25, 2026 at 01:54:26PM +0300, Andy Shevchenko wrote:
> > On Fri, Sep 25, 2026 at 12:30:07PM +0200, Lorenzo Pieralisi wrote:  
> > > On Fri, Sep 25, 2026 at 12:49:54PM +0300, Andy Shevchenko wrote:  
> > > > On Fri, Sep 25, 2026 at 09:48:01AM +0200, Lorenzo Pieralisi wrote:  
> > 
> > ...
> >   
> > > > > +static int acpi_static_fwnode_read_u32_prop_index(const struct fwnode_handle *fwnode,
> > > > > +						  const char *propname,
> > > > > +						  unsigned int index, u32 *value)
> > > > > +{
> > > > > +	u32 *values;
> > > > > +	int ret, count;
> > > > > +
> > > > > +	count = fwnode_property_count_u32(fwnode, propname);
> > > > > +	if (count < 0)
> > > > > +		return count;
> > > > > +
> > > > > +	if (index >= count)
> > > > > +		return -ENOENT;
> > > > > +
> > > > > +	values = kcalloc(count, sizeof(*values), GFP_KERNEL);
> > > > > +	if (!values)
> > > > > +		return -ENOMEM;
> > > > > +
> > > > > +	ret = fwnode_property_read_u32_array(fwnode, propname, values, count);
> > > > > +	if (!ret)
> > > > > +		*value = values[index];  
> > > > 
> > > > Use standard pattern, id est
> > > > 
> > > > 	if (ret)
> > > > 		...
> > > >   
> > > > > +	kfree(values);  
> > > > 
> > > > You want to use __free()
> > > >   
> > > > > +	return ret;
> > > > > +}  
> > > > 
> > > > I believe the whole approach is suboptimal, if you wish get indexed value (but why?)  
> > > 
> > > Why what (that's what the irq_get() interface requires ?) I agree it is
> > > suboptimal - the whole point of the series is an RFC on using properties
> > > to store GSI number/flags, then how to read them we will optimize it
> > > when/if we agree that's the approach to be taken.  
> > 
> > Why to have indexed APIs. The callers usually do not want a single item from an
> > array, they want all of them or a big pile (exception is the array of strings,
> > but we have matching functions for that).
> > 
> > As per approach, this patch is against device property and I don't think we are
> > going to agree on the approach taken in *this* patch.  
> 
> Coming back to this, what is needed here is a way to stash the GSI number,
> flags and name in stardard storage (like OF nodes IRQ properties, ACPI objects
> _CRS, etc).
> 
> To give you some background, I thought about adding an array of:
> 
> GSI [number, flags, name]
> 
> to the ACPI static fwnode itself. Then basically the irq_get() API has got
> all the information it needs from the primary fwnode; while doing that I
> thought that this might have been a bit like reinventing software nodes
> (granted, software node properties are ways more general that what I suggest
> above and I don't expect any other property to be ever added to static fwnodes)
> that's why I put together the series as it is, precisely to understand what's
> best.
> 
> When you say "against device property", what do you mean precisely ?
> 
> I suppose you mean that this approach goes against software node properties
> usage guidelines ?

For what it's worth I like it.  Clean (ish) solution for a messy problem.
May well be some details that can be done differently though.

Just to provide a counter point to Andy :)

Jonathan


> 
> Anyway, again, it is just to provide some context, we are talking about
> a bunch of platform devices, it is nice to have a generic solution but
> it has to be simple enough too given its scope, I understand very well
> your concern with this approach as-is - it is there to find a way
> forward together and show what the problem is.
> 
> Thanks,
> Lorenzo
> 
> > > > it needs to be retrieved as that in the guts of ACPI. Allocating memory for the whole
> > > > array to retrieve a single element is simply wrong.  
> > 
> > ...
> >   
> > > > > +#define ACPI_IRQ_PROP_GSI		"linux,acpi-gsi"
> > > > > +#define ACPI_IRQ_PROP_GSI_TRIGGER	"linux,acpi-gsi-trigger"
> > > > > +#define ACPI_IRQ_PROP_GSI_POLARITY	"linux,acpi-gsi-polarity"  
> > > > 
> > > > Oh... This sounds like a big ugly hack.  
> > > 
> > > That does not help much I am afraid.
> > > 
> > > What's a ugly hack ? Property names ? Using properties for this purpose ?  
> > 
> > Yes, properties started with "linux," for some core functionality.
> > Yes, using properties for this also doesn't sound right. I think the problem
> > here is in the table specifications or somewhere that deep. That's why we
> > ended up in this series.
> >   
> > > Again, it is an RFC for this specific reason and I mentioned that in the
> > > cover letter, thank you for your inputs.  
> > 
> > And here we have a discussion started :-)
> > 
> > P.S. Looks like I was too quick to jump into this thread. I will wait for
> > others to share their view on all this.
> > 
> > -- 
> > With Best Regards,
> > Andy Shevchenko
> > 
> >   
>