Re: [PATCH 5/5] ACPI: Add support for platform bus type

[Yinghai Lu]

On Thu, Nov 1, 2012 at 2:21 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
>> So you are going to replace acpi_device/acpi_driver with
>> platform_device/platform_driver ?
>
> Not exactly.  Let me start from the big picture, though. :-)
>
> First off, we need to unify the handling of devices by the ACPI subsystem
> regardless of whether they are on a specific bus, like PCI, or they are
> busless "platform" devices.
>
> Currently, if a device is on a specific bus *and* there is a device node in the
> ACPI namespace corresponding to it, there will be two objects based on
> struct device for it eventually, the "physical node", like struct pci_dev, and
> the "ACPI node" represented by struct acpi_device.  They are associated with
> each other through the code in drivers/acpi/glue.c.  In turn, if the device is
> busless and not discoverable natively, we only create the "ACPI node" struct
> acpi_device thing for it.  Those ACPI nodes are then *sometimes* bind to
> drivers (represented by struct acpi_driver).
>
> The fact that the busless devices are *sometimes* handled by binding drivers
> directly to struct acpi_device while the other devices are handled through
> glue.c confuses things substantially and causes problems to happen right now
> (for example, acpi_driver drivers sometimes attempt to bind to things that have
> other native drivers and should really be handled by them).
> Furthermore, the situation will only get worse over time if we don't do
> anything about that, because we're going to see more and more devices that
> won't be discoverable natively and will have corresponding nodes in the ACPI
> namespace and we're going to see more buses whose devices will have such
> nodes.
>
> Moreover, for many of those devices there are native drivers present in
> the kernel tree already, because they will be based on IP blocks used in
> the current hardware (for example, we may see ARM-based systems based on
> exactly the same hardware with ACPI BIOSes and without them).  That applies
> to busless devices as well as to devices on specific buses.
>
> Now, the problem is how the unification is going to be done and I honestly
> don't think we have much *choice* here.  Namely, for PCI (and other devices
> discoverable natively) we pretty much have to do the glue.c thing (or something
> equivalent), because we need to match what we've discovered natively against
> the information from the ACPI tables in the BIOS.  This means that for busless
> devices we need to create "physical" nodes as well, so that all of them are
> handled by drivers binding to the "physical" node rather than to struct
> acpi_device.  This also will allow us to reuse the existing drivers with
> minimum modifications (well, hopefully).

ok, acpi_driver will be killed at first.

acpi_pci_root_driver will be converted to platform driver or
add acpi_pci_host_bridge to work with pci_host_bridge.

BTW,  the problem for hotadd pci root bus,
the acpi_driver ops.add can pci root bus and create pci dev before all
acpi device get
created still there.
    https://lkml.org/lkml/2012/10/5/569
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