RE: [PATCH v3 0/7] Rework device probing

["Morten Brørup" <mb@smartsharesystems.com>]

> From: David Marchand [mailto:david.marchand@redhat.com]
> Sent: Saturday, 11 April 2026 12.11
> 
> On Fri, 10 Apr 2026 at 16:35, Morten Brørup <mb@smartsharesystems.com>
> wrote:
> >
> > Is there a workaround until this patch is added, if I don't want
> rte_eal_init() to probe any devices, but I want my application to probe
> devices later by calling rte_bus_scan() followed by rte_bus_probe()?
> >
> > It's not something we really need, so if you don't know it off the
> top of your head, don't spend time trying to figure it out.
> 
> Well, starting from the well known -a pci:0000:00:00.0 trick, I wrote
> an incomplete workaround implemented for OVS.
> https://patchwork.ozlabs.org/project/openvswitch/patch/20260226172429.2
> 12034-3-david.marchand@redhat.com/
> 
> Incomplete, because some buses make life harder with some additional
> parsing restraints (bus/dpaa is the first one that comes to mind) or
> requiring a driver handling the device exists (bus/platform which has
> *no* in-tree driver, though this is a different story..).

Thanks for all the input, David.

In my case it's only PCI bus devices, so I found a relatively simple workaround instead of using the "-a" trick.

I start by not binding the devices to the vfio-pci kernel driver.
Then I call rte_eal_init(); and the devices are not detected by the EAL at this point.
Then I bind the devices to the vfio-pci kernel driver.
And finally I call rte_bus_scan() and rte_bus_probe(); then the devices are detected at this point.

Note: I have to pass "--iova-mode pa" to EAL init.
Otherwise EAL init chooses VA mode, causing my drivers to not load, with the following message:
"PCI_BUS:   Expecting 'PA' IOVA mode but current mode is 'VA', not initializing"

For anyone following the thread...

During experimentation, I observed that if the devices were bound to the vfio-pci kernel driver, and "-a ..." was passed to rte_eal_init() it did - as expected - not load the drivers.
However, when calling rte_bus_scan() and rte_bus_probe() afterwards, the drivers were also not auto-detected at this point.
I guess the "-a ..." parameter is sticky, which makes sense.

Anyway, looking forward to the --no-auto-probing EAL option. :-)