From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Thu, 03 Jul 2014 20:53:06 +0200 Subject: Android and compatibility with deprecated armv7 instructions In-Reply-To: <20140703184626.GC21086@arm.com> References: <4840595.cpHbY6hJKL@wuerfel> <20140703184626.GC21086@arm.com> Message-ID: <15521199.3bNj4354Mf@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thursday 03 July 2014 19:46:26 Will Deacon wrote: > > My initial objections when this was posted were primarily driven by not > knowing when we can safely remove a feature. The default position with the > arm64 kernel was not to emulate anything, then we would see whether we ever > had valid users of these features and could consider them on a case-by-case > basis. I still think that was the right thing to do. > > However, saying "as long as anybody is using it" is really saying "as long > as anybody is complaining about it being missing". Once we've added > emulation, nobody will ever complain about it being missing, because it > won't be missing. Do you have any ideas about phasing out emulation code > when you don't know if it's used or not? Not a lot of good ideas. One thing that can be done is to move the Kconfig option for enabling the emulation under 'CONFIG_EXPERT' in a couple of years, possibly renaming it a few times every other year so people that blindly reuse their .config files will have it disabled again. If we do that, there should of course be a message printed that references a description for how to turn it back on and report that you are still using it. It's certainly a very lengthy process. Just look at how long NWFPE has been in the kernel after it has become obsolete. Arnd