On Mon, 2013-01-28 at 13:58 +0100, Rafael J. Wysocki wrote:
> On Thursday, January 24, 2013 01:26:56 AM Rafael J. Wysocki wrote:
> > Hi All,
> >
> > There is a considerable amount of confusion in the ACPI subsystem about what
> > ACPI drivers are used for. Namely, some of them are used as "normal" device
> > drivers that bind to devices and handle them using ACPI control methods
> > (like
> > the fan or battery drivers), but some of them are just used for handling
> > namespace events, such as the creation or removal of device nodes (I guess
> > it
> > would be fair to call that an abuse of the driver core). These two roles
> > are
> > quite distinct, which is particularly visible from the confusion about the
> > role
> > of the .remove() callback.
> >
> > For the "normal" drivers this callback is simply used to handle situations
> > in
> > which the driver needs to be unbound from the device, because one of them
> > (either the device or the driver) is going away. That operation can't
> > really
> > fail, it just needs to do the necessary cleanup.
> >
> > However, for the namespace events handling "drivers" .remove() means that
> > not
> > only the device node in question, but generally also the whole subtree
> > below it
> > needs to be prepared for removal, which may involve deleting multiple device
> > objects belonging to different bus types and so on and which very well may
> > fail
> > (for example, those devices may be used for such things like swap or they
> > may be
> > memory banks used by the kernel and it may not be safe to remove them at the
> > moment etc.). Moreover, for these things the removal of the "driver"
> > doesn't
> > really make sense, because it has to be there to handle the namespace
> > events it
> > is designed to handle or else things will go remarkably awry in some places.
> >
> > To resolve all that mess I'd like to do the following, which in part is
> > inspired
> > by the recent Toshi Kani's hotplug framework proposal and in part is based
> > on
> > some discussions I had with Bjorn and others (the code references made
> > below are
> > based on the current contens of linux-pm.git/linux-next).
> >
> > 1) Introduce a special data type for "ACPI namespace event handlers" like:
> >
> > struct acpi_scan_handler {
> > const struct acpi_device_id *ids;
> > struct list_head list_node;
> > int (*attach)(struct acpi_device *adev);
> > int (*untie)(struct acpi_device *adev);
> > int (*reclaim)(struct acpi_device *adev);
> > void (*detach)(struct acpi_device *adev);
> > };
>
> After some reconsideration I think that the "untie" and "reclaim" things won't
> be really useful at this level. This means that I only need ACPI scan
> handlers
> to do .attach() and .detach() and all of that becomes really simple, so I
> don't
> see reason to wait with that change.
That's great. I agree with you. The name of attach/detach() also
clarifies the purpose of the interfaces well.
Thanks,
-Toshi
ps.
I am tied up this week and will be somewhat slow to respond...
>
> The following patches introduce ACPI scan handlers and make some use of them.
>
> [1/4] Introduce struct acpi_scan_handler for configuration tasks depending on
> device IDs.
>
> [2/4] Make ACPI PCI root driver use struct acpi_scan_handler.
>
> [3/4] Make ACPI PCI IRQ link driver use struct acpi_scan_handler.
>
> [4/4] Use struct acpi_scan_handler for creating platform devices enumerated
> via ACPI.
>
> Thanks,
> Rafael
>
>
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