Re: [dpdk-dev] [PATCH v6 1/8] eal: pci: add api to rd/wr pci bar region

[Santosh Shukla <sshukla@mvista.com>]

On Tue, Feb 2, 2016 at 2:19 PM, Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> On Tue, Feb 02, 2016 at 06:50:18AM +0100, David Marchand wrote:
>> On Tue, Feb 2, 2016 at 6:43 AM, Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
>> > On Tue, Feb 02, 2016 at 09:44:14AM +0530, Santosh Shukla wrote:
>> >> Current use-case is virtio: It is used as io_bar which is first
>> >> bar[1]. But implementation is generic, can be used to do rd/wr for
>> >> other bar index too. Also vfio facilitate user to do rd/wr to pci_bars
>> >> w/o mapping that bar, So apis will be useful for such cases in future.
>> >>
>> >> AFAIU: uio has read/write_config api only and Yes if bar region mapped
>> >> then no need to do rd/wr, user can directly access the pci_memory. But
>> >> use-case of this api entirely different: unmapped memory by
>> >> application context i.e.. vfio_rd/wr-way {pread/pwrite-way}.
>> >>
>> >> Is above explanation convincing? Pl. let me know.
>> >
>> > TBH, not really. So, as you stated, it should be generic APIs to
>> > read/write bar space, but limiting it to VFIO only and claiming
>> > that read/write bar space is not support by other drivers (such
>> > as UIO) while in fact it can (in some ways) doesn't seem right
>> > to me.
>> >
>> > Anyway, it's just some thoughts from me. David, comments?
>>
>> >From the very start, same opinion.
>> We should have a unique api to access those, and eal should hide
>> details like kernel drivers (uio, vfio, whatever) to the pmd.
>>
>> Now the thing is, how to do this in an elegant and efficient way.
>
> I was thinking that we may just make it be IO port specific read/
> write functions:
>

Ok,

>         rte_eal_pci_ioport_read(dev, bar, buf, size)
>         {
>
>                 return if not an IO bar;
>
>                 if (has io)
>                         return inb/w/l();
>

In that case, It may be r / if (has io) / if (drv->kdrv == UIO)

>                 if (vfio)
>                         return vfio_ioport_read();
>
>                 else, claim aloud that io port read is not allowed
>         }
>
> Let us not handle memory bar resource here: in such case, you should
> go with rte_eal_pci_map_device() and do it with memory mapped io.
>
> Does that make any sense?
>
I am not entirely sure.
Are you considering IGB_UIO, UIO_GENERIC and NIC_UIO: all the cases ?


>         --yliu