linux-kernel - Re: [PATCH 1/2] sparc32,leon: Build with -mcpu=leon3 for SPARC

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Date:   Wed, 29 Nov 2017 13:38:25 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     andreas@...sler.com
Cc:     sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        software@...sler.com
Subject: Re: [PATCH 1/2] sparc32,leon: Build with -mcpu=leon3 for SPARC_LEON

From: Andreas Larsson <andreas@...sler.com>
Date: Tue, 14 Nov 2017 15:03:42 +0100

> Apart from using LEON3 instruction timing it allows for usage of the
> CASA instruction.
> 
> Signed-off-by: Andreas Larsson <andreas@...sler.com>

Up until this point the LEON kconfig option is largely passive.

All of the sparc_cpu_type logic drives what parts of the kernel are
used based upon the run-time detected cpu type.

But with this change, it completely breaks the 32-bit sparc kernel
on any non-Leon processor.

I wish you would reconsider this approach, and instead do hardcoded
assembler instruction opcodes to use "casa" in assembler, and run
time detect CAS support in the 32-bit cpu.

Thank you.