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SubjectRe: [PATCH 3/3] ACPI: Evaluate _CRS while creating device node objects
On Mon, Nov 12, 2012 at 10:03:56PM +0100, Rafael J. Wysocki wrote:
> > > +static acpi_status acpi_bus_add_resource(struct acpi_resource *res,
> > > + void *context)
> > > +{
> > > + struct list_head *list = context;
> > > + struct acpi_resource_list_entry *entry;
> > > +
> > > + entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > > + if (!entry)
> > > + return AE_NO_MEMORY;
> > > +
> > > + entry->resource = *res;
> >
> > This does not work well with all resource types - specifically those that
> > contain pointers, like acpi_resource_gpio and acpi_resource_source.
>
> Good point.
>
> Well, this pretty much means we can't copy those things.

Yeah. I only noticed this yesterday when I tested the GPIO translation in a
custom driver (since it uses the acpi_resource_gpio).

> > The memory for the resources gets freed once acpi_walk_resources() is done.
>
> I know that.
>
> Having to evaluate _CRS and creating a buffer, converting the output into
> ACPI resources and so on every time we need to look into the device's current
> resources is totally inefficient. We _need_ to cache the _CRS output.

I agree and besides having adev->resources is much easier to use than
calling acpi_walk_resources() everytime.

> Now, because of the pointers in certain types of resources, we can't
> make copies of the resource objects used by acpi_walk_resources() which
> makes that function totally unuseful to us.
>
> I suppose we can just do acpi_get_current_resources() and play with the
> buffer returned by it. That won't be nice, but still better than what we
> have.

I don't know any better option.

Thanks.


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