Re: [dpdk-dev] [EXT] Re: [PATCH v2 1/7] lib/librte_pci: add rte_pci_regs.h

[Manish Chopra <manishc@marvell.com>]

> -----Original Message-----
> From: Gaëtan Rivet <grive@u256.net>
> Sent: Thursday, July 16, 2020 11:26 PM
> To: Thomas Monjalon <thomas@monjalon.net>
> Cc: Jerin Jacob <jerinjacobk@gmail.com>; Manish Chopra
> <manishc@marvell.com>; Ferruh Yigit <ferruh.yigit@intel.com>; Igor
> Russkikh <irusskikh@marvell.com>; dpdk-dev <dev@dpdk.org>
> Subject: [EXT] Re: [dpdk-dev] [PATCH v2 1/7] lib/librte_pci: add
> rte_pci_regs.h
> 
> External Email
> 
> ----------------------------------------------------------------------
> On 16/07/20 18:57 +0200, Thomas Monjalon wrote:
> > 16/07/2020 18:43, Jerin Jacob:
> > > On Thu, Jul 16, 2020 at 9:25 PM Thomas Monjalon
> <thomas@monjalon.net> wrote:
> > > >
> > > > 16/07/2020 15:02, Jerin Jacob:
> > > > > On Thu, Jul 16, 2020 at 6:20 PM Thomas Monjalon
> <thomas@monjalon.net> wrote:
> > > > > >
> > > > > > 16/07/2020 13:55, Jerin Jacob:
> > > > > > > On Thu, Jul 16, 2020 at 4:57 PM Thomas Monjalon
> <thomas@monjalon.net> wrote:
> > > > > > > >
> > > > > > > > 16/07/2020 12:27, Jerin Jacob:
> > > > > > > > > On Thu, Jul 16, 2020 at 3:48 PM Gaëtan Rivet
> <grive@u256.net> wrote:
> > > > > > > > > >
> > > > > > > > > > On 16/07/20 12:08 +0200, Gaëtan Rivet wrote:
> > > > > > > > > > > Re-CCing dev@dpdk.org as it was removed from the reply.
> > > > > > > > > > >
> > > > > > > > > > > On 13/07/20 08:13 -0700, Manish Chopra wrote:
> > > > > > > > > > > > This is merely copy of latest linux/pci_regs.h in
> > > > > > > > > > > > order to avoid dependency of dpdk on user headers.
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > I guess this dependency is an issue on non-linux
> > > > > > > > > > > systems, when you must use those defines in a
> > > > > > > > > > > generic implementation. Can you confirm this is the
> motivation here?
> > > > > > > > > > >
> > > > > > > > > > > If so, I think it would be clearer to state "in
> > > > > > > > > > > order to avoid dependency of DPDK on linux headers".
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > To add to it, if this is actually the motivation to
> > > > > > > > > > add this header, I don't think it is sufficient.
> > > > > > > > > >
> > > > > > > > > > You can restrict the function definition to the linux
> > > > > > > > > > part of the PCI bus driver instead, using stubs for other
> systems.
> > > > > > > > > >
> > > > > > > > > > > > Signed-off-by: Manish Chopra <manishc@marvell.com>
> > > > > > > > > > > > Signed-off-by: Igor Russkikh
> > > > > > > > > > > > <irusskikh@marvell.com>
> > > > > > > > > > > > ---
> > > > > > > > > > > >  drivers/bus/pci/linux/pci_uio.c     |    2 +-
> > > > > > > > > > > >  drivers/bus/pci/linux/pci_vfio.c    |    2 +-
> > > > > > > > > > > >  drivers/net/bnx2x/bnx2x.h           |    2 +-
> > > > > > > > > > > >  drivers/net/hns3/hns3_ethdev_vf.c   |    2 +-
> > > > > > > > > > > >  drivers/vdpa/ifc/base/ifcvf_osdep.h |    2 +-
> > > > > > > > > > > >  lib/librte_pci/Makefile             |    1 +
> > > > > > > > > > > >  lib/librte_pci/meson.build          |    2 +-
> > > > > > > > > > > >  lib/librte_pci/rte_pci_regs.h       | 1075
> +++++++++++++++++++++++++++
> > > > > > > > > > > >  8 files changed, 1082 insertions(+), 6
> > > > > > > > > > > > deletions(-)  create mode 100644
> > > > > > > > > > > > lib/librte_pci/rte_pci_regs.h
> > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > [...]
> > > > > > > > > > >
> > > > > > > > > > > > diff --git a/lib/librte_pci/rte_pci_regs.h
> > > > > > > > > > > > b/lib/librte_pci/rte_pci_regs.h new file mode
> > > > > > > > > > > > 100644 index 000000000..1d11f4de5
> > > > > > > > > > > > --- /dev/null
> > > > > > > > > > > > +++ b/lib/librte_pci/rte_pci_regs.h
> > > > > > > > > > > > @@ -0,0 +1,1075 @@
> > > > > > > > > > > > +/* SPDX-License-Identifier: GPL-2.0 WITH
> > > > > > > > > > > > +Linux-syscall-note */
> > > > > > > > > > > > +/*
> > > > > > > > > > >
> > > > > > > > > > > This file is delivered alongside the PCI lib, targeting
> userspace.
> > > > > > > > > > > This seems to be an exception to the license policy
> > > > > > > > > > > described in license/README. Code shared between
> > > > > > > > > > > kernel and userspace is expected to be dual-licensed BSD-3
> and GPL-2.0.
> > > > > > > > > > >
> > > > > > > > > > > As it is a copy of Linux user includes, re-licensing
> > > > > > > > > > > it as BSD-3 as well is not possible.
> > > > > > > > > > >
> > > > > > > > > > > So I think it might require a techboard + governing
> > > > > > > > > > > board exception approval. Ferruh or Thomas, what do you
> think?
> > > > > > > > >
> > > > > > > > > I think, instead of importing GPL-2.0 file, We can add
> > > > > > > > > the constants as need by the DPDK as symbols start from
> > > > > > > > > RTE_PCI_*(It will fix up the namespace as well).
> > > > > > > >
> > > > > > > > If symbols can be found in /usr/include/, don't add anything.
> > > > > > >
> > > > > > > Not by default on all the distros. It is part of pciutils library.
> > > > > > > Moreover, we need these symbols for Windows OS as well.
> > > > > > > IMO, We should add absolute minimum constants that needed
> > > > > > > for DPDK as RTE_PCI_*
> > > > > >
> > > > > > I am for mandating the dependency instead of copying it.
> > > > >
> > > > > You mean _pciutils_ package as a mandatory dependency to  DPDK.
> > > >
> > > > There is already this dependency:
> > > >         #include <linux/pci_regs.h>
> > >
> > > I just checked in archlinux, PCI headers can be provided by
> > >
> > > # pacman -F /usr/include/pci/header.h usr/include/pci/header.h is
> > > owned by core/pciutils 3.7.0-
> > >
> > > # pacman -F /usr/include/linux/pci.h usr/include/linux/pci.h is
> > > owned by core/linux-api-headers 5.4.17-1
> > >
> > >
> > > > I'm missing the real justification for this patch.
> > >
> > > See below.
> > >
> > > > Is there some missing definitions?
> > > > Is there some environments where this file is missing?
> > > >
> > > > > > pciutils cannot be installed on Windows?
> > > > > > Why do you care about Windows?
> > > > > > I don't see any contribution for qede on Windows.
> > > > >
> > > > > You closely review the patch, it not about qede. The proposed
> > > > > file comes at lib/librte_pci/rte_pci_regs.h which is common to
> Windows.
> > > >
> > > > The series is for qede. I'm trying to understand the motivation.
> > >
> > > First version of qede driver sent with defined generic PCI symbols
> > > and generic PCI function like pci_find_next_ext_capability() in qede
> driver.
> >
> > That's a pity the v2 is not threaded with v1, I would have found these
> > explanations easily myself.
> >
> > > In the review, I suggested using generic rte_ function as
> > > a) It is not specific to qede.
> > > b) Other drivers also doing the same thing in their own driver space
> > > as there is no dpdk API for the same.
> > > This patches create generic API for pci_find_next_ext_capability()
> > > and remove duplicate implementation from the drivers.
> > > https://urldefense.proofpoint.com/v2/url?u=http-3A__patches.dpdk.org
> > >
> _patch_73959_&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=bMTgx2X48QVX
> yXOEL8
> > > ALyI4dsWoR-m74c5n3d-
> ruJI8&m=eNuzGYhB7u2Wzru3VeBTY7QDZSSb9VQ9eQXW56D4
> > > 64Y&s=eatY5xyw-474yS0cBJXyG7gLyPXFo243P2LmBDDsXd8&e=
> >
> > I agree it's good to have an API for such thing.
> >
> > So far such feature is supported in drivers on Linux, requiring only
> > Linux headers to be installed.
> > Do we need more?
> >
> >
> 
> +1 to make it generic, no question here.
> 
> On linux, the dependency is already there (either from linux headers or
> pciutils) to have the original. So including this header in DPDK is only useful
> for other OSes.
> 
> I think right now we should only add pci_find_next_ext_capability() full
> implementation within linux part of PCI bus, other systems being stubs.
> 
> We can go with your suggestion Jerin about adding only the specific symbols
> needed, prefixed with RTE_, once we decide to have windows support.
> Question is whether we need it right now. Is there a driver that would make
> use of it support more than linux currently?
> 
> --

I don't know if there are any drivers which will require this other than linux as of today - 

My only motivation of adding these symbols in dpdk via rte_pci_regs.h (new file in lib/librte_pci/) was to avoid any dependency of dpdk on /usr/include/../pci_regs.h,
since I was little unsure whether in all distributions (linux/windows) supported will have the required PCI defines available in /usr/include/../pci_regs.h file or not in order
to implement rte_pci_find_next_ext_capability().  (unless user to bound for updating headers by mean of installing any latest _pciutils_/packages). Moreover, for not just
this API, but if going forward if we have to add any new APIs which could rely/depend on PCI defines availability under /usr/include.

From the discussion so far - 

1. Define the function under drivers/bus/pci/linux/pci.c only and add empty/stub implementation for windows/pci.c and bsd/pci.c ?
2.  Just relying on /usr/include/ is perfectly okay without adding any defines anywhere for now ?, it will just require <linux/pci_regs.h> inclusion in
     drivers/bus/pci/linux/pci.c. OR Shall I add (may be in lib/librte_pci/rte_pci.h ?) only required PCI defines with RTE_ prefixed and use them instead ?

Thanks,
Manish