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

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

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:

	rte_eal_pci_ioport_read(dev, bar, buf, size)
	{

		return if not an IO bar;

		if (has io)
			return inb/w/l();

		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?

	--yliu