linux-kernel - Re: [PATCH 2/2] [RFC] arm64: Add dependencies to vendor-specific errata

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Message-ID: <CAMuHMdXO5Qv1XezGW+yELOaTkoFUA4B8SvBpBH=r4mLtbnkBhg@mail.gmail.com>
Date:   Thu, 16 Apr 2020 18:18:42 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <agross@...nel.org>, Wei Xu <xuwei5@...ilicon.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Robert Richter <rrichter@...vell.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] [RFC] arm64: Add dependencies to vendor-specific errata

Hi Mark,

On Thu, Apr 16, 2020 at 5:57 PM Mark Rutland <mark.rutland@....com> wrote:
> On Thu, Apr 16, 2020 at 05:38:07PM +0200, Geert Uytterhoeven wrote:
> > And perhaps you do want to enable some platform-specific drivers for
> > VFIO pass-through?  Hence having ARCH_* dependencies on those drivers
> > means they cannot be enabled :-( Hmm...
>
> IIRC platform device passthrough requires an corresponding VFIO platform
> driver in the host to handle reset and so on, but it does seem a shame

If your SoC has a reset controller, that problem has been solved in a generic
way, cfr. "[PATCH v5] vfio: platform: Add generic reset controller support"
(https://lore.kernel.org/lkml/20181113131508.18246-1-geert+renesas@glider.be/).
Unfortunately not yet upstream.

Combine with "hw/arm/sysbus-fdt: Add support for instantiating generic devices"
(https://github.com/geertu/qemu/commit/180318003c08594e8e852b2285a98184f905bfa9)
and you're set ;-)

> to not allow the user to select a driver if they really want it.

I forgot you can add "|| VIRTIO_MMIO" to the dependencies of drivers for
devices that can be used with VFIO pass-through.

> I guess there might be platform-specific PCIe drivers too, which might
> work with VFIO regardless.

Indeed. PCI is business as usual.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds