Re: [PATCH] eal: map io resources for non x86 architectures

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

On Fri, Dec 18, 2015 at 01:24:41PM +0530, Santosh Shukla wrote:
> >> I guess we have done enough evaluation / investigation that suggest -
> >> so to map iopci region to userspace in arch agnostic-way -
> >>
> >> # either we need to modify kernel
> >>                - Make sure all the non-x86 arch to support mapping for
> >> iopci region (i.e. pci_mmap_page_range). I don;t think its a correct
> >> approach though.
> >>             or
> >>                - include /dev/ioport char-mem device file who could do
> >> more than byte operation, Note that this implementation does not exist
> >> in kernel.  I could send an RFC to lkml.
> >
> > Maybe you could propose the two to lkml, to get some feedbacks from
> > those kernel/ARM gurus? Please cc me if you do so.
> >
> 
> The latter one I already shared old lkml thread, Pl. revisit my v1 0/6
> patch [1] and in that refer [2].

Oops, sorry, a bit busy, that I didn't look at it carefully. My bad,
anyway.

> Josh has already proposed to lkml but for some reason thread didn't
> went far. I can restart that discussion giving dpdk use-case as an
> example/ requirement.

I had a quick go through of the discussion. Both hpa and Arnd seem
to be fine with the ioctl interface on /dev/port. Have you tried
that?  And if you want to restart it, ioctl might be a better option
than /dev/ioport, judging from the discussion.

> 
> And for the former one, I'll have to check with linux-arm why iopci
> region not mappable. By grepping kernel source all i could see two
> commit - latest one is 415ae101 and older one 1da177e. Both has
> nothing to explain why
> if (mmap_state == pci_mmap_io)
>       return -EINVAL;
> 
> Setting pci io region to -EINVAL, should have fundamental reason for
> sure. But we'll have to check, for that I could post as a query rather
> a patch to lkml.

No idea, such check should have been there in the very beginning
for some reason. And here is a quote from Arnd:

    Only powerpc, microblaze, alpha, sparc and xtensa allow
    users to mmap I/O space, even though a lot of others could. 

> 
> Note that dpdk already has out-of-tree implementation for
> dom0/xen-case too, it creates special device file which maps pci
> resources. so keep one more igb_uio char device so to map iopci region
> wont hurt much though!

Xen is not a good example here; I'm even not sure it still works
or not :)

	--yliu
> [1] http://permalink.gmane.org/gmane.comp.networking.dpdk.devel/29531
> 
> >         --yliu
> >>
> >> OR keep device file in user space (current approach)
> >> Right now Virtio-for-arm patches are blocked on this, let me know if
> >> someone has better approach/thought in mind.
> >>
> >> Thanks.
> >>
> >> > Then we can try a pci_mmap solution or, as you suggest, an interface in
> >> > drivers/char/mem.c
> >> >