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Date: Wed, 20 Jan 2016 14:22:43 +0000
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Tomasz Nowicki <tn@semihalf.com>
Cc: bhelgaas@google.com, arnd@arndb.de, will.deacon@arm.com,
	catalin.marinas@arm.com, rjw@rjwysocki.net, hanjun.guo@linaro.org,
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Subject: Re: [PATCH V3 11/21] pci, acpi: Move ACPI host bridge device
 companion assignment to core code.
Message-ID: <20160120142243.GB13437@red-moon>
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On Wed, Jan 20, 2016 at 02:40:08PM +0100, Tomasz Nowicki wrote:

[...]

> >>>>+	/* Root bridge device needs to be sure of parent ACPI type */
> >>>>+	ACPI_COMPANION_SET(&device->dev, device);
> >>>
> >>>I do not understand why the code above is needed, can you elaborate
> >>>please ?
> >>>
> >>
> >>This makes sure that device->dev can be identified as ACPI device,
> >>so we can use to_acpi_device_node() and assign companion safely
> >>below.
> >
> >I do not follow. If you refer to the fwnode handle type, that is
> >already set by ACPI core code (before acpi_pci_root_add() is called,
> >in acpi_init_device_object()).
> 
> acpi_init_device_object() sets ACPI fwnode handle type only for
> "device", but not for "device->dev" which is what is passed as an
> argument to pci_create_root_bus().
> 
> Without ACPI_COMPANION_SET(&device->dev, device) here, no one can be
> sure if we have ACPI device in pci_create_root_bus().

Ok, got it. The question is whether this should be done in ACPI
core instead (is there a reason why it should *not* be done ?), but I
now understand your point.

Thanks,
Lorenzo