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Date:   Wed, 28 Mar 2018 16:04:53 +0800
From:   Guo Ren <ren_guo@c-sky.com>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Jason Cooper <jason@lakedaemon.net>,
        c-sky_gcc_upstream@c-sky.com, gnu-csky@mentor.com,
        thomas.petazzoni@bootlin.com, wbx@uclibc-ng.org
Subject: Re: [PATCH 15/19] csky: Build infrastructure
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Hi Arnd,

On Wed, Mar 28, 2018 at 09:40:49AM +0200, Arnd Bergmann wrote:
> Ok, thanks for the clarification. Obviously if they are mutually incompatible,
> there is no point in using a common kernel, so your current version is
> absolutely fine, and this is similar to how we cannot have a common kernel
> between ARMv5, ARMv7-A and ARMv7-M, which are all incompatible
> at the kernel level.
Yes.

> One more question for my understanding: Are the three types of ck8xx
> CPUs mutually incompatible in user space as well, or are the differences
> only for the kernel? For the ARM example, ARMv5 and ARMv7
> fundamentally require separate kernels, but both can run user space
> programs built for ARMv5.

 -mcpu=ck807 app could run on ck807, ck810, ck860.
 -mcpu=ck810 app could run on ck807, ck810, ck860.
 -mcpu=ck860 app only  run on ck860.

They are all incompatible at the kernel level.

Best Regards
 Guo Ren