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

From: Arnd Bergmann <arnd@arndb.de>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	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 15:36:39 +0200	[thread overview]
Message-ID: <CAK8P3a3HkXotBFVfbL3iaqUAM2ENpBKh7gy+hXH8TXsZHPfwTQ@mail.gmail.com> (raw)
In-Reply-To: <20200416125630.GF4987@lakrids.cambridge.arm.com>

On Thu, Apr 16, 2020 at 2:56 PM Mark Rutland <mark.rutland@arm.com> wrote:
> On Thu, Apr 16, 2020 at 01:56:58PM +0200, Geert Uytterhoeven wrote:
> > Currently the user is asked about enabling support for each and every
> > vendor-specific erratum, even when support for the specific platform is
> > not enabled.
> >
> > Fix this by adding platform dependencies to the config options
> > controlling support for vendor-specific errata.
> >
> > Note that FUJITSU_ERRATUM_010001 is left untouched, as no config symbol
> > exists for the Fujitsu A64FX platform.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>
> I'm not su1re that it makes sense to do this in general, becaose the
> ARCH_* platform symbols are about plactform/SoC support (e.g. pinctrl
> drivers), and these are (mostly) CPU-local and/or VM-visible.
>
> I think that it makes sense for those to be independent because:
>
> * future SoCs in the same family might not need the same CPU errata
>   workarounds, and it's arguably just as confusing to have the option
>   there.
>
> * It prevents building a minimal VM image with all (non-virtualized)
>   platform support disabled, but all possible (VM-visible) errata
>   options enabled. I do that occassionally for testing/analysis, and I
>   can imagine this is useful for those building images that are only
>   intended to be used in VMs.

Most architectures over time grow a CPU selection option that is
at least somewhat orthogonal to the platform selection. I think so far
arm64 has intentionally resisted this based on the idea that the CPUs
are mostly equal and differences are better handled at runtime.

If we decide to revisit this in the future that might help both the
errata selection and give a way to e.g. build for an ARMv8.2
baseline.
This does seem pretty far out at the moment of course, given
that most SoCs we work on are still based on Cortex-A53 or A72 ;-)

> I think the change to SOCIONEXT_SYNQUACER_PREITS makes sense given
> that's a platform-level detail. Arguably that should be moved into
> drivers/irqchip/Kconfig.

Agreed

       Arnd