linux-kernel - Re: [PATCH V3 11/21] pci, acpi: Move ACPI host bridge device companion assignment to core code.

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Message-ID: <20160127174222.GA9982@red-moon>
Date:	Wed, 27 Jan 2016 17:42:22 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Tomasz Nowicki <tn@...ihalf.com>, rjw@...ysocki.net
Cc:	rjw@...ysocki.net, bhelgaas@...gle.com, arnd@...db.de,
	will.deacon@....com, catalin.marinas@....com,
	hanjun.guo@...aro.org, okaya@...eaurora.org,
	jiang.liu@...ux.intel.com, Stefano.Stabellini@...citrix.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....com, ddaney@...iumnetworks.com, tglx@...utronix.de,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jchandra@...adcom.com, jcm@...hat.com
Subject: Re: [PATCH V3 11/21] pci, acpi: Move ACPI host bridge device
 companion assignment to core code.

On Wed, Jan 20, 2016 at 03:41:56PM +0100, Tomasz Nowicki wrote:
> On 20.01.2016 15:22, Lorenzo Pieralisi wrote:
> >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.
> >
> 
> I am not able to answer that question, but I see lots of changes in
> this area made by Rafael.

I had a further look and I am not sure why the fwnode_handle* in the
dev member of the acpi_device is not made to point at the fwnode member
of the acpi_device by *default* (acpi_init_device_object() ?), probably
because it is never used as such but certainly Rafael knows, so I would
ask him to clarify please it is unclear to me.

I do not see anything wrong in what you are doing in this patch.

Rafael, any comments ?

Thanks,
Lorenzo