Re: [dpdk-dev] [PATCH v7 2/2] bus/pci: support MMIO in PCI ioport accessors

["谢华伟(此时此刻）" <huawei.xhw@alibaba-inc.com>]

On 2021/2/25 17:52, David Marchand wrote:
> On Thu, Feb 25, 2021 at 5:00 AM 谢华伟(此时此刻） <huawei.xhw@alibaba-inc.com> wrote:
>>>>> Is the 'outb_p' to 'outb' conversion intentional? And if so why?
>>>>>
>>>>> Same of the all 'outb_p', 'outw_p', 'outl_p'.
>>>> There is no need to delay for virtio device, as we can see in virtio
>>>> legacy driver.
>>>>
>>>> IMO, the delay is for ugly old device. The device itself should
>>>> assure the previous IO completes when the subsequent IO instruction
>>>> arrives.
>>>>
>>> Can there be any virtio legacy device needing this?
>> The pause version delays sometime by writing to 0x80 debug port. virtio
>> doesn't need this. virtio legacy PMD driver doens't use this.
>>
>> Any device relying on this i think is buggy. How could the device rely
>> on some uncertain cpu cycles to behave correct?
>>
>>> What is the downside of using "pause until the I/O completes" versions?
>> The downside in virtio PMD is a small performance penalty when we use it
>> to notify backend. CPU executes unnecessary serializing IO instruction.
>>
>> I check kernel code, io wrapper for in/out doesn't use p version.
> This change is a fix/optimisation.
> This is a separate topic from adding MMIO support with x86 ioport.
> I would split as a separate patch.

Hi David:

Maybe there is confuse? There is no change. The out/in is added. I don't 
remove _p on purpose.

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