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

[David Marchand <david.marchand@6wind.com>]

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.


Regard,
-- 
David Marchand