From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Sun, 8 Dec 2013 04:39:45 +0100 Subject: [PATCH] ARM: clean-up common multi-platform kconfig options In-Reply-To: <20131207181052.GR4360@n2100.arm.linux.org.uk> References: <1386262722-26016-1-git-send-email-robherring2@gmail.com> <20131207181052.GR4360@n2100.arm.linux.org.uk> Message-ID: <201312080439.46063.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Saturday 07 December 2013, Russell King - ARM Linux wrote: > So, as far as I'm aware, today, a kernel which has V6, V6K and V7 > will work across all those CPUs. > > What's rather annoying in this thread is that you and Arnd are running > around seemingly making decisions on this without bothering to find out > the details, in persuit of endless cleanups. Where is this heading? I admit that we've been stumbling a bit in the dark at some points, but that doesn't mean every idea ends up in a patch that even gets submitted. What I've concluded so far is (please correct any statements that you find are wrong): * there is no harm in "select HAVE_SMP if CPU_V7" for multiplatform, as was the original suggestion. Whether we want to actually do that is open for discussion when someone submits a patch. * It was a mistake (I guess mine) to 'select CPU_V6' from ARCH_MULTI_V6, since that makes V6K based platforms slower without a reason, and we probably want to do something else. * A kernel which enables V6, V6K and V7 has a broken kuser_cmpxchg64 implementation on pre-V6K CPUs. * Most platforms (possibly every one but OMAP2) that select CPU_V6 today are actually V6K compatible. It's probably worth asking those V6 platform maintainers to change their CPU selection after confirming that they are V6K-only. * I'm still trying to understand the full implications of CONFIG_CPU_USE_DOMAIN, but according to the comment in 247055aa21ffe "ARM: 6384/1: Remove the domain switching on ARMv6k/v7 CPUs", it seems to be a bug to enable this on v6k or v7 CPUs, which we currently do whenever CPU_V6 (implied by CONFIG_MULTI_V6) is enabled. Arnd