[PATCH 1/2] doc: announce region based device mapping support

[Sunil Kumar Kori]

Hi Chenbo,

There are pci devices which has huge BAR memory but might not be used completely.
Like PCIe device DDR memory is exposed over BAR with 32Gb or so.
So in that case user might have a requirement to mmap only areas of its interest.
Also avoid wasting of extra memory for each pages when kernel mmaps it.

Yes, it is similar to sparse mmap in vfio but I didn't find any support in DPDK for sparse mmap. 
So I picked this approach but in either case, ABI change notification is needed, Right?

Regards
Sunil Kumar Kori

> -----Original Message-----
> From: Xia, Chenbo <chenbo.xia at intel.com>
> Sent: Thursday, July 7, 2022 6:09 PM
> To: Sunil Kumar Kori <skori at marvell.com>; Ray Kinsella <mdr at ashroe.eu>
> Cc: dev at dpdk.org
> Subject: [EXT] RE: [PATCH 1/2] doc: announce region based device mapping
> support
> 
> External Email
> 
> ----------------------------------------------------------------------
> Hi Sunil,
> 
> > -----Original Message-----
> > From: skori at marvell.com <skori at marvell.com>
> > Sent: Tuesday, June 28, 2022 9:54 PM
> > To: Ray Kinsella <mdr at ashroe.eu>
> > Cc: dev at dpdk.org; Sunil Kumar Kori <skori at marvell.com>
> > Subject: [PATCH 1/2] doc: announce region based device mapping support
> >
> > From: Sunil Kumar Kori <skori at marvell.com>
> >
> > Adding region based device mapping support, which enables pci device
> > to map only required memory region instead of mapping full BAR.
> 
> Why there will be such requirement to mmap only part of BAR when the BAR
> can be fully mmapped. I thought you want to enable something like sparse
> mmap feature in VFIO, but seems it's a feature that let driver ask for specific
> mmap option. Could you explain the use case here?
> 
> Thanks,
> Chenbo
> 
> >
> > Signed-off-by: Sunil Kumar Kori <skori at marvell.com>
> > ---
> >  doc/guides/rel_notes/deprecation.rst | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/doc/guides/rel_notes/deprecation.rst
> > b/doc/guides/rel_notes/deprecation.rst
> > index 4e5b23c53d..8800a3eb41 100644
> > --- a/doc/guides/rel_notes/deprecation.rst
> > +++ b/doc/guides/rel_notes/deprecation.rst
> > @@ -125,3 +125,16 @@ Deprecation Notices
> >    applications should be updated to use the ``dmadev`` library instead,
> >    with the underlying HW-functionality being provided by the ``ioat`` or
> >    ``idxd`` dma drivers
> > +
> > +* pci: Update ``rte_pci_device`` and ``rte_pci_driver`` to add region
> > based
> > +  memory mapping support. There could be a requirement to mmap
> > + specific
> > memory
> > +  region only. Using this mechanism, pci device can be mapped for  a
> > + given BAR at a given offset of given size.
> > +
> > +  ``rte_pci_device`` will be added with following field
> > + ``regions[PCI_MAX_RESOURCE][PCI_MAX_REGION_PER_RESOURCE];``.
> This
> > + field
> > will
> > +  specify the regions which are mapped for a given BAR.
> > +
> > +  ``rte_pci_driver`` will be added with ``rte_pci_region_map
> > + *regions``
> > and
> > +  ``valid_bars[PCI_MAX_RESOURCE]``. Using these fields, driver can
> > propagate
> > +  its region information which are required to be mmap.
> > --
> > 2.25.1