linux-kernel - Re: [PATCH] ARM: ep93xx: don't use clang IAS for crunch

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Date:   Fri, 26 Feb 2021 12:47:03 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Alexander Sverdlin <alexander.sverdlin@...il.com>,
        "soc@...nel.org" <soc@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        Hartley Sweeten <HartleyS@...ionengravers.com>
Subject: Re: [PATCH] ARM: ep93xx: don't use clang IAS for crunch

On Fri, Feb 26, 2021 at 11:32 AM Hartley Sweeten
<HartleyS@...ionengravers.com> wrote:
>
> On Friday, February 26, 2021 12:23 PM, Alexander Sverdlin wrote:
> > On Fri, 2021-02-26 at 17:43 +0100, Arnd Bergmann wrote:
> >> Randconfig builds with ep93xx fail with the clang integrated assembler
> >> that does not understand the maverick crunch extensions:
> >>
> >> arch/arm/mach-ep93xx/crunch-bits.S:94:2: error: invalid instruction
> >>  cfstr64 mvdx0, [r1, #0] @ save 64b registers
> >>
> >> It is unclear if anyone is still using support for crunch: gcc-4.8
> >> dropped it in 2012 when it was already too broken to be used
> >> reliabled. glibc support existed as an external patch but was never merged upstream.
> >> We could consider removing the last bits of the kernel support as well.
> >
> > This was my impression already in 2006, that Cirrus is not going to work on Crunch support. From my PoV it's OK to remove the support in the kernel completely.
>
> Martin Guy did a lot of work trying to get the maverick crunch working but I was never able to successfully use it for anything. It "kind" of works but depending on the EP93xx silicon revision there are still a number of hardware bugs that either give imprecise or garbage results.
>
> I have no problem with removing the kernel support for the maverick crunch.

Either way, please consider adding a

Link: https://github.com/ClangBuiltLinux/linux/issues/1272

tag. That will help us notice when/where this lands in order to close
out the issue. Thanks for the patch.

(if we go with this rather than removing the driver:)
Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>

(I'm also fine with removing the driver; my ack is not conditional on
one way or the other).
-- 
Thanks,
~Nick Desaulniers