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

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Andy Gross <agross@kernel.org>, Wei Xu <xuwei5@hisilicon.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Robert Richter <rrichter@marvell.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/2] [RFC] arm64: Add dependencies to vendor-specific errata
Date: Thu, 16 Apr 2020 18:18:42 +0200	[thread overview]
Message-ID: <CAMuHMdXO5Qv1XezGW+yELOaTkoFUA4B8SvBpBH=r4mLtbnkBhg@mail.gmail.com> (raw)
In-Reply-To: <20200416155655.GA7155@lakrids.cambridge.arm.com>

Hi Mark,

On Thu, Apr 16, 2020 at 5:57 PM Mark Rutland <mark.rutland@arm.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@linux-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