[dpdk-dev] [PATCH v9 0/2] support both PIO and MMIO BAR for legacy device in virtio PMD

[谢华伟(此时此刻）]

On 2021/3/4 2:24, Stephen Hemminger wrote:
> On Thu, 04 Mar 2021 01:46:50 +0800
> "谢华伟(此时此刻）"<huawei.xhw at alibaba-inc.com>  wrote:
>
>> virtio PMD assumes legacy device only supports PIO BAR resource. This is wrong.
>> As we need to create lots of devices, as PIO resource on x86 is very limited,
>> we expose MMIO(memory IO) BAR.
>>
>> Kernel supports both PIO and MMIO BAR for legacy virtio-pci device, and for all
>> other pci devices. This patchset handles different type of BAR in the similar way.
>>
>> In previous implementation, under igb_uio driver we get PIO address from igb_uio
>> sysfs entry; with uio_pci_generic, we get PIO address from /proc/ioports for x86,
>> and for other ARCHs, we get PIO address from standard PCI sysfs entry.
>> For PIO/MMIO RW, there is different path for different drivers and arch.
> Just to add some background. At the time virtio for DPDK was developed,
> the kernel only supported legacy mode, and it required I/O ports on x86.

Hi Stephen:

Do you mean QEMU?  I think QEMU exports PIO by default.

For kernel, I checked 3.10 code at hand, virtio legacy driver doesn't 
assume I/O port. It uses generic API pci_iomap and ioread/write.

>
> One concern is that, you should make sure these patches still work on
> the oldest releases of Linux kernel that DPDK supports. For upstream
> kernel that should be 4.4 kernel (oldest currently maintained LTS).
> The Linux system requirements doc file needs update!
>
> For distributions, the oldest version would be probably be RHEL 7.

PIO is verified on Redhat 7.9 (3.10.0-1160.11.1.el7.x86_64).

As this patch uses the generic kernel exported interface, which all 
other PMDs have been using, i think it doesn't break compatibility.