linux-kernel - Re: [PATCH v3 00/32] provide interfaces to access PCIe capabilities registers

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Date:	Mon, 20 Aug 2012 23:47:36 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Don Dutile <ddutile@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"Rafael J . Wysocki" <rjw@...k.pl>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Yijing Wang <wangyijing@...wei.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v3 00/32] provide interfaces to access PCIe capabilities
 registers

On 08/20/2012 11:35 PM, Bjorn Helgaas wrote:
> On Mon, Aug 20, 2012 at 9:26 AM, Jiang Liu <liuj97@...il.com> wrote:
>> On 08/14/2012 12:25 PM, Bjorn Helgaas wrote:
>>> On Wed, Aug 1, 2012 at 8:54 AM, Jiang Liu <liuj97@...il.com> wrote:
>>>> From: Jiang Liu <liuj97@...il.com>
>>>>
>>>> As suggested by Bjorn Helgaas and Don Dutile in threads
>>>> http://www.spinics.net/lists/linux-pci/msg15663.html, we could improve access
>>>> to PCIe capabilities register in to way:
>>>> 1) cache content of PCIe Capabilities Register into struct pce_dev to avoid
>>>>    repeatedly reading this register because it's read only.
>>>> 2) provide access functions for PCIe Capabilities registers to hide differences
>>>>    among PCIe base specifications, so the caller don't need to handle those
>>>>    differences.
>>>>
>>>> This patch set applies to
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git pci-next
>>>
>>> Would you mind rebasing this to v3.6-rc1?  I think you posted this
>>> when my branch was still 3.5-based, and there are some upstream
>>> changes that cause minor conflicts here.
>>>
>>> You currently have:
>>>
>>>     int pci_pcie_capability_change_word(struct pci_dev *dev, int pos,
>>> u16 set_bits, u16 clear_bits)
>>>
>>> I think this is a bit awkward because the function name doesn't
>>> suggest *how* the word will be changed, and the clearing happens
>>> before the setting (opposite the parameter order).  Something like:
>>>
>>>     int pci_pcie_capability_mask_and_set_word(..., u16 mask, u16 set) or
>>>     int pci_pcie_capability_clear_and_set_word(..., u16 clear, u16 set)
>>>
>>> would be more obvious.  If you use "mask_and_set", I think the
>>> function should do "(val & mask) | set" with the complement being at
>>> the call site.  If you use "clear_and_set", I think it's OK to do
>>> "(val & ~mask) | set" as in your current patch.
>>>
>>> I know I suggested the "pci_pcie_capability_*" names, but they're
>>> getting a bit unwieldy, especially if we do "mask_and_set" or similar.
>>>  There are already several "pcie_*" functions, so maybe we should
>>> drop the leading "pci_" from these and just have:
>>>
>>>     pcie_capability_read_word
>>>     pcie_capability_write_word
>>>     pcie_capability_mask_and_set_word
>>>
>>> Bjorn
>>>
>> Hi Bjorn,
>>         I have made following changes according to your suggestions,
>>         1) get rid of the "pci_" prefix for access functions.
>>         2) rename pci_pcie_capability_change_{word|dword}() to
>>         pcie_capability_clear_and_set_{word|dword}.
>>         3) add pcie_capability_{set|clear}_{word|dword}().
> 
> Are 2) and 3) really the same?  If they're really different, we'll end up with:
> 
>     pcie_capability_clear_and_set_word()
>     pcie_capability_clear_and_set_dword()
>     pcie_capability_set_word()
>     pcie_capability_set_dword()
>     pcie_capability_clear_word()
>     pcie_capability_clear_dword()
> 
> It seems a little excessive to have all six interfaces, since the
> first two are sufficient to provide all the functionality.
> 
Hi Bjorn,
	pcie_capability_{set|clear}_{word|dword}() are implemented as inline functions
which just call pcie_capability_clear_and_set_{word|dword}(). If it seems a little redundant,
I could help to remove them.
	Regards!
	Gerry


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