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

On Tue, Feb 2, 2016 at 6:43 AM, Yuanhan Liu [off-list ref] wrote:

On Tue, Feb 02, 2016 at 09:44:14AM +0530, Santosh Shukla wrote:

quoted

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.


Regard,
-- 
David Marchand