linux-kernel - Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI domain

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Date:	Wed, 10 Sep 2014 09:44:51 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Liviu Dudau <Liviu.Dudau@....com>
CC:	Rob Herring <robherring2@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	"Jason Gunthorpe" <jgunthorpe@...idianresearch.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Will Deacon" <Will.Deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci <linux-pci@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"Suravee Suthikulanit" <suravee.suthikulpanit@....com>,
	linux-arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Device Tree ML" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI
 domain_nr

>> OK. Sorry, I have one last question, because domain will be used to calculate the address used to
>> access PCI hardware config registers. So if DTS file doesn't report the domain, how do we know
>> we would access the right registers when we use the auto increment domain vaule ?
> 
> That's a good question and sides with Arnd's suggestion to try to mandate the presence of the PCI
> domain in the DTS. However, by grepping through the source code, it looks like the architectures
> that use the domain number for reading config registers (x86-based) are non-DT architectures,
> while DT-aware arches seem to ignore the domain number except when printing out messages. Is that
> another confirmation that most DT-aware architectures have only run with domain_nr = 0?
> 

Arnd's suggestion is make sense to me, thanks for Bjorn's detailed explanation, now I know domain_nr
is purely internal to kernel in DT-aware platform, it's not needed when access PCI config space.

Thanks!
Yijing.

> 
>> Has there a mechanism to make sure system can access the correct registers by the domain ?
> 
> Not as such if you look with x86 glasses. With the exception of powerpc all other architecures
> seem to happily assume domain_nr = 0 and ignore it in the computation of configuration registers
> offsets.
> 
> Best regards,
> Liviu
> 
>>
>> Thanks!
>> Yijing.
>>
>>>
>>> Best regards,
>>> Liviu
>>>
>>>>
>>>> PCI get domain by ACPI "_SEG" in IA64(drivers/acpi/pci_root.c)
>>>> ......
>>>> 	status = acpi_evaluate_integer(handle, METHOD_NAME__SEG, NULL,
>>>> 				       &segment);
>>>> 	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>>>> 		dev_err(&device->dev,  "can't evaluate _SEG\n");
>>>> 		result = -ENODEV;
>>>> 		goto end;
>>>> 	}
>>>> .......
>>>>
>>>> Thanks!
>>>> Yijing.
>>>>
>>>>>
>>>>>> This function
>>>>>> is just a weird mixture of data retrieval and allocation. I think you
>>>>>> need to separate it into 2 functions.
>>>>>
>>>>> It is meant to do allocation with the retrieval being a short-cut (or fine
>>>>> control if you want).
>>>>>
>>>>> I need to think a bit more for a better solution.
>>>>>
>>>>> Best regards,
>>>>> Liviu
>>>>>
>>>>>>
>>>>>> Rob
>>>>>>
>>>>>
>>>>
>>>>
>>>> -- 
>>>> Thanks!
>>>> Yijing
>>>>
>>>>
>>>
>>
>>
>> -- 
>> Thanks!
>> Yijing
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
>> the body of a message to majordomo@...r.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 


-- 
Thanks!
Yijing

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