Re: [PATCH v1 2/4] ACPI: PCI: Introduce acpi_dev_get_pci_dev()

[Rafael J. Wysocki (Intel)]

On Wed, Jul 15, 2026 at 5:56 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, Jul 15, 2026 at 05:16:19PM +0200, Rafael J. Wysocki wrote:
>
> > Some acpi_get_pci_dev() callers already have a struct ACPI device for
> > which they want to get the struct pci_dev pointer of the associated
> > PCI device, so they don't need to look for one.
> >
> > For this reason, add acpi_dev_get_pci_dev() that will get a PCI device
> > for a given ACPI one (if possible) and turn acpi_get_pci_dev() into
> > a static inline helper passing the acpi_fetch_acpi_dev() return value
> > directly to acpi_dev_get_pci_dev().
>
> ...
>
> >  /**
> > - * acpi_get_pci_dev - convert ACPI CA handle to struct pci_dev
> > - * @handle: the handle in question
> > + * acpi_dev_get_pci_dev - Get a struct pci_dev for a given ACPI device
> > + * @adev: Target ACPI device.
> >   *
> > - * Given an ACPI CA handle, the desired PCI device is located in the
> > - * list of PCI devices.
> > + * Get the first PCI device associated with @adev, if present, and bump up its
>
> What is the meaning of the "first PCI device" in terms of ACPI specification (and
> implementation in the Linux kernel)? I think it's impossible case to have more
> than one object to be a companion to a PCI device. Am I wrong?

The ACPI specification is kind of agnostic to that.

In the kernel, there can be multiple physical devices associated with
one ACPI device object, but I agree that every PCI device has at most
one ACPI companion.

I'll drop the word "first" from this comment.

> > + * reference counter.
> >   *
> > - * If the device is found, its reference count is increased and this
> > - * function returns a pointer to its data structure.  The caller must
> > - * decrement the reference count by calling pci_dev_put().
> > - * If no device is found, %NULL is returned.
> > + * Callers are responsible for dropping the PCI device reference obtained by
> > + * this function.
> > + *
> > + * Return: The struct pci_dev pointer of a reference-counted PCI device on
> > + * success or NULL on failure.
> >   */
>
> --