linux-kernel - Re: [PATCH V5 07/15] pci, acpi: Provide generic way to assign bus domain number.

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Date:	Wed, 17 Feb 2016 16:05:41 +0100
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	Jayachandran Chandrashekaran Nair 
	<jayachandran.chandrashekaran@...adcom.com>
Cc:	Bjorn Helgaas <helgaas@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	will.deacon@....com, catalin.marinas@....com, rafael@...nel.org,
	hanjun.guo@...aro.org,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	okaya@...eaurora.org, jiang.liu@...ux.intel.com,
	Jayachandran Chandrashekaran Nair <jchandra@...adcom.com>,
	Stefano.Stabellini@...citrix.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....com, ddaney@...iumnetworks.com,
	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,
	jcm@...hat.com
Subject: Re: [PATCH V5 07/15] pci, acpi: Provide generic way to assign bus
 domain number.

On 17.02.2016 15:21, Jayachandran Chandrashekaran Nair wrote:
> On Wed, Feb 17, 2016 at 7:37 PM, Tomasz Nowicki <tn@...ihalf.com> wrote:
>> On 17.02.2016 14:44, Jayachandran Chandrashekaran Nair wrote:
>>>
>>> Tomasz, Lorenzo,
>>>
>>> On Tue, Feb 16, 2016 at 7:23 PM, Tomasz Nowicki<tn@...ihalf.com>  wrote:
>>>>
>>>>> As we now have valid PCI host bridge device reference we can
>>>>> introduce code that is going to find its bus domain number using
>>>>> ACPI _SEG method.
>>>>>
>>>>> Note that _SEG method is optional, therefore _SEG absence means
>>>>> that all PCI buses belong to domain 0.
>>>>>
>>>>> While at it, for the sake of code clarity we put ACPI and DT domain
>>>>> assign methods into the corresponding helpers.
>>>
>>> In my patchset, I had a slightly different and I think better approach for
>>> this without calling the _SEG method again. Please see
>>> http://www.spinics.net/lists/arm-kernel/msg478167.html
>>> at the last part ofhttp://www.spinics.net/lists/arm-kernel/msg478169.html
>>
>> Relying on NULL parent device to make decision on boot method is really ugly
>> way. This may hit us again once we want to obtain another firmware specific
>> info e.g. numa node. IMO we need to fix it this way.
>
> I am not relying on NULL there, in the current code parent is NULL
> in case of ACPI, and the check is needed not to crash (unless that
> has changed).

This series passes down valid parent, see [PATCH V5 06/15].

>
> The main part was the macro acpi_pci_get_segment() and the use
> of acpi_pci_root_info from sysdata to do this.

Since we can obtain related firmware specific data from valid parent 
device (without defining another accessors), I do not see the point to 
use sysdata. Let me know your opinion.

Tomasz