RE: [PATCH v12 04/16] baseband/acc: introduce PMD for ACC200

["Chautru, Nicolas" <nicolas.chautru@intel.com>]

Hi Thomas, 

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> 08/11/2022 00:52, Chautru, Nicolas:
> > Hi Thomas,
> > Reminder : do you mind kindly clarifying/confirming below. Then we can
> update the docs accordingly. Thanks.
> >
> > From: Chautru, Nicolas
> > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > 31/10/2022 16:43, Chautru, Nicolas:
> > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > > 12/10/2022 19:59, Nicolas Chautru:
> > > > > > > +Bind PF UIO driver(s)
> > > > > > > +~~~~~~~~~~~~~~~~~~~~~
> > > > > > > +
> > > > > > > +Install the DPDK igb_uio driver, bind it with the PF PCI
> > > > > > > +device ID and use ``lspci`` to confirm the PF device is
> > > > > > > +under use by ``igb_uio`` DPDK
> > > > > > UIO driver.
> > > > > >
> > > > > > igb_uio is not recommended.
> > > > > > Please focus on VFIO first.
> > > > > >
> > > > > > > +The igb_uio driver may be bound to the PF PCI device using
> > > > > > > +one of two methods for ACC200:
> > > > > > > +
> > > > > > > +
> > > > > > > +1. PCI functions (physical or virtual, depending on the use
> > > > > > > +case) can be bound to the UIO driver by repeating this
> > > > > > > +command for every
> > > > function.
> > > > > > > +
> > > > > > > +.. code-block:: console
> > > > > > > +
> > > > > > > +  cd <dpdk-top-level-directory>  insmod
> > > > > > > + ./build/kmod/igb_uio.ko echo "8086 57c0" >
> > > > > > > + /sys/bus/pci/drivers/igb_uio/new_id
> > > > > > > +  lspci -vd8086:57c0
> > > > > > > +
> > > > > > > +
> > > > > > > +2. Another way to bind PF with DPDK UIO driver is by using
> > > > > > > +the ``dpdk-devbind.py`` tool
> > > > > > > +
> > > > > > > +.. code-block:: console
> > > > > > > +
> > > > > > > +  cd <dpdk-top-level-directory>
> > > > > > > + ./usertools/dpdk-devbind.py -b igb_uio 0000:f7:00.0
> > > > > > > +
> > > > > > > +where the PCI device ID (example: 0000:f7:00.0) is obtained
> > > > > > > +using lspci -vd8086:57c0
> > > > > >
> > > > > > This binding is not specific to the driver.
> > > > > > It would be better to refer to the Linux guide instead of
> > > > > > duplicating it again and again.
> > > > > >
> > > > > > > +In a similar way the PF may be bound with vfio-pci as any PCIe
> device.
> > > > > >
> > > > > > You could mention igb_uio here.
> > > > > > Is there any advantage in using igb_uio?
> > > > > >
> > > > >
> > > > > Igb_uio is arguably easier to use to new user tend to start with
> > > > > it or specific
> > > > ecosystem. This is typically the entry point (no iommu, no flr
> > > > below the bonnet, no vfio token...) hence good to have a bit of
> > > > handholding with a couple of lines capturing how to easily run a
> > > > few tests. I don't believe this is too redundant to have these few
> > > > lines compared to the help in bring to the user not having to double guess
> their steps.
> > > > > More generally there are a number of module drivers combinations
> > > > > that are
> > > > supported based on different deployments. We don't document in too
> > > > much details for the details since that is not too ACC specific
> > > > and there is more documentation no pf_bb_config repo for using the
> > > > PMD from
> > > the VF..
> > > > >
> > > > > Basically Thomas let us know more explicitly what you are
> > > > > suggesting as
> > > > documentation update. You just want more emphasis on vfio-pci flow
> > > > (which is fair, some of it documented on pf_bb_config including
> > > > the vfio token passing but we can reproduce here as well) or something
> else?
> > > >
> > > > There are 2 things to change:
> > > > 1/ igb_uio is going to be deprecated, so we must emphasize on VFIO
> > >
> > > Is there a date for deprecation? Do you mean to EOL the dpdk-kmods
> > > repository itself; or something more specific for DPDK code like
> > > removing RTE_PCI_KDRV_IGB_UIO; or last to just take out from
> documentation?
> 
> There is no final decision yet, but the techboard wishes we focus more on VFIO
> which is in Linux upstream.
> Out-of-tree module (like igb_uio) is not recommended.
> 
> > > It tends to be historical but uio has value notably for ease of use.
> 
> I don't think it is easy to use an out-of-tree module.
> It needs to be compiled and installed.

That is more up to the user. For some users/ecosystems it can be genuinely significantly easier and also historical deployments still to be supported. 
Even if vfio-pci is the focus for most deployments. 
But mentioning that since you are thinking about removing support, I see value keeping support for a bit still

> 
> > > 2/ for doc
> > > > maintenance, it is better to have common steps described in one place.
> > > > If needed, you can change the common doc and refer to it.
> > >
> > > Do you mean to remove these sections and just add a pointer to
> > > https://doc.dpdk.org/guides/linux_gsg/linux_drivers.html instead in
> > > all these bbdev PMDS?
> 
> Yes
> If the Linux guide is not convenient, I suggest to improve it.
> 
> > > Please kindly confirm. I see specific steps for binding in many
> > > other PMDs docs in DPDK, a bit redundant but provides simple steps
> > > specific to a PMD in one place. I don't mind either way.
> 
> The other PMD docs should point to a common doc.
> 
> Redundant docs make very hard to update.
> 

OK, did an update on this v1 for your review
https://patches.dpdk.org/project/dpdk/patch/20221108234325.45589-2-nicolas.chautru@intel.com/
the warning from checkpatch is a false alarm

Thanks
Nic