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 16:35:30 +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 <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 <Stefano.Stabellini@...citrix.com>,
	robert.richter@...iumnetworks.com, Marcin Wojtas <mw@...ihalf.com>,
	Liviu.Dudau@....com, David Daney <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 16:21, Jayachandran Chandrashekaran Nair wrote:
> On Wed, Feb 17, 2016 at 8:35 PM, Tomasz Nowicki <tn@...ihalf.com> wrote:
>> 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.
>
> In the patch, you use the parent info and call _SEG method again.
> The segment information is available in the ->root->segment of
> acpi_pci_root_info if you setup the sysdata like in my patch

I know it is in sysdata->root->segment, but the way it is passed down is 
wrong. sysdata is the pointer to unknown content (void *) so we need to 
validate it before we can use it. If we merge this patch we can remove 
first _SEG call.

Tomasz