linux-kernel - Re: [PATCH 10/15] soc: octeontx2: Reconfig MSIX base with IOVA

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Message-ID: <CA+sq2CepUamZzjc8XS7gPALW3=19W2uv3hq=SUa86+i-oGsGnw@mail.gmail.com>
Date:   Fri, 31 Aug 2018 00:09:04 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, olof@...om.net,
        LAKML <linux-arm-kernel@...ts.infradead.org>,
        linux-soc@...r.kernel.org, Geetha sowjanya <gakula@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>, tglx@...utronix.de,
        Marc Zyngier <marc.zyngier@....com>, jason@...edaemon.net,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 10/15] soc: octeontx2: Reconfig MSIX base with IOVA

On Thu, Aug 30, 2018 at 7:23 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Tue, Aug 28, 2018 at 3:17 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> > On Tue, Aug 28, 2018 at 6:27 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > On Tue, Aug 28, 2018 at 2:42 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> > > > On Tue, Aug 28, 2018 at 5:39 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > > On Tue, Aug 28, 2018 at 12:58 PM <sunil.kovvuri@...il.com> wrote:
> > > >
> > > > This admin function is a PCI device which is capable of provisioning
> > > > HW blocks to other PCIe SRIOV devices in the system. Each HW block
> > > > (eg memory buffer pools, NIC dewscriptors, crypto engines e.t.c) needs
> > > > certain no of MSIX vectors. Admin function has a set of 32K MSIX vectors
> > > > in memory (not on-chip) which based on HW block provisioning to a PCI device
> > > > attaches the required number of vectors to that device. Some part of this
> > > > configuration is done by low level firmware.
> > > >
> > > > RVU_AF_MSIXTR_BASE points to the memory region allocated for 32K MSIX
> > > > vectors. If kernel is booted with IOMMU enabled and admin function device
> > > > is attached to SMMU, HW will go through translation to access this MSIX
> > > > vector memory region. Hence the mapping done in this patch.
> > >
> > > Do you mean this is not a regular PCIe MSI-X interrupt to the GIC, but
> > > something internal to your device that gets routed through the IOMMU
> > > back into the device?
> > >
> >
> > This is a regular PCIe MSI-X interrupt, the difference is that the
> > bunch of PCI devices
> > here doesn't have a fixed set of MSIX vectors. Admin function has a
> > memory region with
> > 32K MSIX vectors which it provisions to PCI devices based on the HW
> > functional blocks
> > attached to them. A PCI device which works as a ethernet device needs
> > X number of vectors
> > and a crypto device needs Y number of vectors.
> >
> > Since the admin function owns the whole MSIX vector region, HW uses
> > this device's stream ID
> > to access the vectors. Hence the IOMMU mapping. Once MSIX vectors are
> > provisioned to
> > a PCI device they work as normal MSIX interrupt like any other device.
>
> Ok, I think I got it now, just to confirm: the MSIX vectors you allocate
> in the admin device refer to memory backing the BAR that contains
> the MSI-X entries of the other functions, right?

Yes, that's correct.

>
> I was a bit confused here and assumed that you were mapping
> the MMIO area of an interrupt controller that receives the interupt
> transactions.
>
>          Arnd