Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200409232728.231527-1-caij2003@gmail.com> <CAK8P3a3uj7AHbAo4sNzr6KQx5Fk6v99k4ZixCgKo1tUuGoat9Q@mail.gmail.com>
 <CAMj1kXGXNxXGiC4dmNXHkZ6n=J0Fhim3oSwNx4Bz5m9fEphJvQ@mail.gmail.com> <20200410123301.GX25745@shell.armlinux.org.uk>
In-Reply-To: <20200410123301.GX25745@shell.armlinux.org.uk>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 13 Apr 2020 12:23:38 -0700
Message-ID: <CAKwvOd=-u3grX3O4CtBayJYhv=mmsxMrRTF=AMcKMbphN5Xkgg@mail.gmail.com>
Subject: Re: [PATCH] ARM: do not assemble iwmmxt.S with LLVM toolchain
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Jian Cai <caij2003@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Peter Smith <Peter.Smith@arm.com>,
        Stefan Agner <stefan@agner.ch>,
        David Howells <dhowells@redhat.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Manoj Gupta <manojgupta@google.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Ilie Halip <ilie.halip@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Steven Rostedt (VMware)" <rostedt@goodmis.org>,
        Jian Cai <jiancai@google.com>,
        Doug Anderson <armlinux@m.disordat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Apr 10, 2020 at 5:33 AM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> For older CPUs, it doesn't matter what the latest ARM ARM says, the
> appropriate version of the ARM ARM is the one relevant for the CPU
> architecture.  This is a mistake frequently made, and it's been pointed
> out by Arm Ltd in the past (before ARMv6 even came on the scene) that
> keeping older revisions is necessary if you want to be interested in
> the older architectures.

As if it never existed *waves hands*.  Interesting.  Does ARM still
distribute these older reference manuals? Do you keep copies of the
older revisions?

>
> However, there's an additional complication here: DEC's license from
> Arm Ltd back in the days of StrongARM allowed them to make changes to
> the architecture - that was passed over to Intel when they bought that
> part of DEC.  Consequently, these "non-Arm vendor" cores contain
> extensions that are not part of the ARM ARM.  iWMMXT is one such
> example, which first appeared in the Intel PXA270 SoC (an ARMv5
> derived CPU).
>
> In fact, several of the features found in later versions of the ARM
> architecture came from DEC and Intel enhancements.
>
> If your compiler/assembler only implements what is in the latest ARM
> ARM, then it is not going to be suitable for these older CPUs and
> alternate vendor "ARM compatible" CPUs.

This is a neat piece of history, thanks for sharing.
-- 
Thanks,
~Nick Desaulniers