[PATCH v3 2/2] pseries/eeh: Add Pseries pcibios_bus_add_device

[Bjorn Helgaas]

On Tue, Oct 17, 2017 at 12:23:01PM -0500, Juan Alvarez wrote:
> On 10/17/17 11:26 AM, Bjorn Helgaas wrote:
> > To pop back up to the top of the stack, I think the main point of this
> > patch is to keep from binding a driver to the VFs in the kernel that
> > set PCI_SRIOV_CTRL_VFE.  This patch does that by setting
> > pdev->match_driver to -1 in powerpc-specific code.
> Correct, to add to your comment, we will only add to the PSeries platform
>  (in PowerPC)  configure SR-IOV path.
> > I think all systems, not just powerpc, want to prevent this VF driver
> > binding, so I hope there's a generic solution that everybody can use.
> The patch that we made this change dependent on:
> 
> https://patchwork.kernel.org/patch/9882915/
> 
> Is a generic form of not binding a pci device to a device driver
> and can be used in another environment if needed.

Right.  But that patch isn't really on the path to inclusion (mainly
because it's test framework and doesn't fix a bug or add support for
new hardware or features).

I'm suggesting that maybe there should be a generic way to prevent
binding to VF devices that works for everybody and doesn't require any
arch-specific code at all.

> >>>> So like existing way of enabling SRIOV we still rely on the PF driver to
> >>>> enable VFs - but in this case the attachment phase is done via a user
> >>>> action via a management console in our case (novalink or hmc) triggered
> >>>> event that will essentially act like a hotplug.
> >>>>
> >>>> So in the fine details of that user triggered action the system
> >>>> firmware will bind the VFs, allowing resources to be allocated to
> >>>> the VF.  - Which essentially does all the attaching as we know it
> >>>> today but is managed by PHYP not by the kernel.
> >>> What exactly does "firmware binding the VFs" mean?  I guess this must
> >>> mean assigning a VF to a partition, injecting a hotplug add event to
> >>> that partition, and making the VF visible in config space?
> >> Firmware basically adds a device node to the device tree as defined
> >> in the (PAPR) Power Architecture Platform Requirements document.
> > From the point of view of the kernel that consumes this device tree
> > and owns the VF, I guess this looks like a hot-add.  
> Correct, this is intended. We want to minimize change and only focus
> on configure SR-IOV path in the PF on PSeries platform.
> > It would be nice
> > if this could be exposed to that kernel by having the firmware inject
> > a normal PCIe hotplug interrupt, but I'm guessing it's not that
> > simple.
>
> I don't understand entirely your suggestion. However, in the case of
> interrupts PHYP owns all the resources and will be associated accordingly
> with a partitionable endpoint (PE).

Assume you have a Linux kernel, and PHYP assigns a VF to it.  What
happens in that Linux kernel?  How does it discover this new device?

I'm suggesting that it would be cool if that kernel received a hotplug
interrupt from the Downstream Port leading to the new VF, and the
pciehp driver could read the Slot Status register and see that
"Presence Detect Changed" was set.  If that happened, the pciehp
driver should automatically enumerate the new device and there
wouldn't be much if any powerpc-specific code in the path.

Bjorn