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Date:   Fri, 13 May 2022 14:29:09 +0200
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Jonas Paulsson <paulsson@linux.vnet.ibm.com>,
        Ulrich Weigand <ulrich.weigand@de.ibm.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Andreas Krebbel <krebbel@linux.ibm.com>,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [PATCH 3/8] s390/entry: shorten OUTSIDE macro
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On Thu, May 12, 2022 at 12:25:01PM -0700, Nick Desaulniers wrote:
> Interesting! Thanks for the links.
> I'm guessing in our CI that we should probably pursue testing some of
> the newer revisions. Wasn't defconfig updated from z10 to z12 not too
> long ago?

Yes, that was 1.5 years ago (commit ac94a2911e84 ("s390: update defconfigs")).

> So probably
> CONFIG_MARCH_Z13
> CONFIG_MARCH_Z14
> CONFIG_MARCH_Z15
> CONFIG_MARCH_Z16
> 
> All look like they're still "supported" (and I'm guessing
> CONFIG_MARCH_Z10 and CONFIG_MARCH_Z196 are not too much burden to
> continue to maintain kernel support for), with a higher emphasis
> perhaps on z15+z16?

That makes sense. However for the kernel it doesn't make a difference
if compiled for z15 or z16 - there were no general instructions added
with z16 that would make any difference for the kernel.
All new instructions that came with z16 are either only relevant for
user space, or used via .insn notation in the kernel, and only used if
some hardware feature is present.