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

[Rafael J. Wysocki]

On Wednesday, November 28, 2012 01:31:39 PM Toshi Kani wrote:
> 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.

Sure.  The complication here is that we'll need to handle the removal of
a bunch of struct acpi_device objects when a whole table goes away.

However, first, we don't seem to handle table unloading now.  At least
acpi_unload_parent_table() is not called from anywhere as far as I can
say.  Second, we'll need to handle the removal of struct acpi_device objects
_anyway_ on table unload, this way or another.

> [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.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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