linux-kernel - Re: [PATCH v3 1/4] ACPI: Support system notify handler via .sys

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Message-ID: <4411201.YLQBH7zWSI@vostro.rjw.lan>
Date:	Wed, 28 Nov 2012 19:28:33 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-acpi@...r.kernel.org, lenb@...nel.org,
	linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
	isimatu.yasuaki@...fujitsu.com, liuj97@...il.com
Subject: Re: [PATCH v3 1/4] ACPI: Support system notify handler via .sys_notify

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. :-)

Thanks,
Rafael


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