linux-kernel - Re: [PATCH v2 3/6] powerpc/pci: use pci_is

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Date:	Fri, 11 Oct 2013 16:22:25 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Gavin Shan <shangw@...ux.vnet.ibm.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Paul Mackerras <paulus@...ba.org>,
	<linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 3/6] powerpc/pci: use pci_is_pcie() to simplify code

>> In my idea, dev->pcie_cap(here is pci_dev->pcie_cap) will update in set_pcie_port_type() function,
>> and this function always be called after allocate pci device. We get pci_dev by eeh_dev_to_pci_dev(),
>> I think pci_dev has been initialized completely.
>>
>>> This function has possibility to be invoked before that. However,
>>> we don't have the binding (eeh device <-> PCI device) for the case.
>>> So the piece of code shouldn't be running
>>
>> In PCI core, I knew
>>
>> pci_scan_device()
>>   pci_setup_device()
>>       set_pcie_port_type()
>>            pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
>>
>> In powerpc, I also found
>>
>> of_scan_pci_dev()
>>   of_create_pci_dev()
>>       set_pcie_port_type()
>> 	    pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
>>>
>>> However, it's a bit safer to have pci_find_capability(dev, PCI_CAP_ID_EXP)
>>> as well even though we needn't it for 99.9% cases if you agree :-)
>>
>> I agree, this function is not the performance bottleneck,
>> safety is more important. :)
>> So if Bjorn and Benjamin think it's not safe, it's ok to drop it. :)
>>
> 
> No, it's not what I mean. Anyway, "v3" looks good to me.
> At least, it can save PCI-CFG access cycles find locate
> the PCIe capability position :-)

Thanks! :)

> 
> Thanks,
> Gavin
> 
> 
> .
> 


-- 
Thanks!
Yijing

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