[PATCH v8 04/14] powerpc/vas: Alloc and setup IRQ and trigger port address

[Oliver O'Halloran]

On Mon, Mar 23, 2020 at 8:28 PM Cédric Le Goater <clg at kaod.org> wrote:
>
> On 3/23/20 10:06 AM, Cédric Le Goater wrote:
> > On 3/19/20 7:14 AM, Haren Myneni wrote:
> >>
> >> Alloc IRQ and get trigger port address for each VAS instance. Kernel
> >> register this IRQ per VAS instance and sets this port for each send
> >> window. NX interrupts the kernel when it sees page fault.
> >
> > I don't understand why this is not done by the OPAL driver for each VAS
> > of the system. Is the VAS unit very different from OpenCAPI regarding
> > the fault ?
>
> I checked the previous patchsets and I see that v3 was more like I expected
> it: one interrupt for faults allocated by the skiboot driver and exposed
> in the DT.
>
> What made you change your mind ?

>From init_vas_inst() in arch/powerpc/platforms/powernv/vas.c:

        if (pdev->num_resources != 4) {
                pr_err("Unexpected DT configuration for [%s, %d]\n",
                                pdev->name, vasid);
                return -ENODEV;
        }

This code should never have been written, but here we are. Due to the
above adding an interrupt in the DT makes the driver unable to bind on
older kernels. In an older version of the patches (don't think it was
posted) Haren was using a non-standard interrupt property and we could
work around the problem by going back to that.

However, we already have the OPAL calls for allocating / freeing
hardware interrupt numbers so why not do that? If we ever want to take
advantage of the job completion interrupts we'd want to have the
ability to allocate them since the completion interrupts are
per-window rather than per-VAS.

> This version is hijacking the lowlevel routines of the XIVE irqchip which
> is not the best approach. OCXL is doing that because it needs to allocate
> interrupts for the user space processes using the AFU and we should rework
> that part.

What'd you have in mind for the reworking the oxcl interrupt
allocation? I didn't find it that objectionable since it's more or
less the same as what happens when allocating IPIs.

> However, the translation fault interrupt is allocated by skiboot.
>
> Sorry for the noise, I would like to understand more how this works. I also
> have passthrough in mind.
>
> C.