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

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Message-ID: <CAK8P3a1BRvhQ9iQWP2hTrJOu+Z+vmmek-Uobw6zX0dM4zFe_gQ@mail.gmail.com>
Date:   Thu, 30 Aug 2018 15:53:25 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-soc@...r.kernel.org, gakula@...vell.com,
        sgoutham@...vell.com, Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Jason Cooper <jason@...edaemon.net>,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 10/15] soc: octeontx2: Reconfig MSIX base with IOVA

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?

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