Re: [PATCH v3 1/4] ACPI: Support system notify handler via .sys_notify

[Toshi Kani <toshi.kani@hp.com>]

On Wed, 2012-11-28 at 19:28 +0100, Rafael J. Wysocki wrote:
> On Wednesday, November 28, 2012 09:54:43 AM Toshi Kani wrote:
> > > > > > > By using acpi_install_notify_handler(), each driver needs to walk
> > > > > > > through the entire ACPI namespace to find its associated ACPI devices
> > > > > > > and call it to register one by one.  I think this is more work for
> > > > > > > non-ACPI drivers than defining acpi_driver.
> > > > > > 
> > > > > > I'm not really sure what you mean.  The drivers in question already know
> > > > > > what the relevant ACPI device nodes are (because they need them anyway
> > > > > > for other purposes), so they don't need to look for them specifically and
> > > > > > acpi_install_notify_handler() doesn't do any namespace walking.  So what
> > > > > > you said above simply doesn't make sense from this viewpoint.
> > > > > 
> > > > > Yes, if drivers already know the relevant ACPI devices, then walking the
> > > > > ACPI namespace is not necessary.  I was referring the case like
> > > > > processor_driver.c, acpi_memhotplug.c, and container.c in my statement. 
> > > > 
> > > > BTW, when an ACPI device is marked as non-present, which is the case
> > > > before hot-add, we do not create an acpi_device object and therefore do
> > > > not bind it with a driver.  This is why these drivers walk the ACPI
> > > > namespace and install their notify handlers regardless of device status.
> > > 
> > > So maybe we should create struct acpi_device objects in that case too?
> > 
> > I think it has some challenge as well.  We bind an ACPI driver with
> > device_register(), which calls device_add()-> kobject_add().  So, all
> > non-present ACPI device objects will show up in sysfs, unless we can
> > change the core.  This will change user interface.  There can be quite
> > many non-present devices in ACPI namespace depending on FW
> > implementation.
> 
> If additional devices appear in sysfs, that's not a problem.  If there
> were fewer of them, that would be a real one. :-)

I see.  I guess this means that once we expose all non-present devices
in sysfs, we cannot go back to the current way.  So, we need to be very
careful.  Anyway, this model requires separate handling for static ACPI
[1] and dynamic ACPI [2], which may make the state model complicated.

1. Static ACPI - No creation / deletion of acpi_device at hot-plug.
2. Dynamic ACPI - Create acpi_device at hot-add, delete at hot-remove.


Thanks,
-Toshi

[1] ACPI namespace is static and contains the maximum possible config. 
[2] ACPI namespace is dynamic. SSDT is loaded at hot-add, and unloaded
at hot-remove.