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Received: from n2100.armlinux.org.uk ([2001:4d48:ad52:3201:214:fdff:fe10:4f86]:59715) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.90_1) (envelope-from ) id 1gZvI1-0000BV-AD; Thu, 20 Dec 2018 10:10:49 +0000 Received: from linux by n2100.armlinux.org.uk with local (Exim 4.90_1) (envelope-from ) id 1gZvHy-0000m3-DQ; Thu, 20 Dec 2018 10:10:46 +0000 Date: Thu, 20 Dec 2018 10:10:44 +0000 From: Russell King - ARM Linux To: linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-omap@vger.kernel.org, linux-oxnas@groups.io, linux-samsung-soc@vger.kernel.org, linux-soc@vger.kernel.org Subject: Re: [PATCH 0/9] Clean up ARM SMP/CPU hotplug implementations Message-ID: <20181220101044.GN9507@n2100.armlinux.org.uk> References: <20181213175952.GC26090@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20181213175952.GC26090@n2100.armlinux.org.uk> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181220_021117_658158_C5ACCB0E X-CRM114-Status: GOOD ( 29.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Barry Song , Lorenzo Pieralisi , Neil Armstrong , Tony Lindgren , Viresh Kumar , Linus Walleij , Manivannan Sadhasivam , Liviu Dudau , Patrice Chotard , Krzysztof Kozlowski , David Brown , Kukjin Kim , Sudeep Holla , Andy Gross , Shiraz Hashim , Andreas =?iso-8859-1?Q?F=E4rber?= Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Since almost no one has responded, my intention is to queue up patches 1-3,5-8 for the Christmas-time merge window through my tree. They will be in linux-next tonight. On Thu, Dec 13, 2018 at 05:59:52PM +0000, Russell King - ARM Linux wrote: > There is a lot of apparent copied code in arch/arm for handling SMP/ > CPU hotplug, much of which is inappropriate or plain buggy. This > seems to be a topic that occasionally comes up. > > The "pen_release" thing was created for ARM Ltd development platforms > where there was no way to individually control secondary CPUs leaving > the boot loader - they all jumped to whatever physical code address > was supplied at the same time. This made it necessary for _these_ > platforms to have a "holding pen" for the CPUs while the kernel > initialised. > > The "boot_lock" thing was also created for ARM Ltd development > platforms which had restricted bus bandwidth, and which used the > loops_per_jiffy delay mechanism, which was calibrated for each > secondary CPU. With the restricted bus bandwidth, activity from the > boot CPU would affect the delay calibration adversely. > > Lastly, the Versatile CPU hotplug implementation is an entirely > ficticious one - these platforms do _not_ support CPU hotplug as > there is no way to actually disable any of the secondary CPUs, or > reset them. Such an implementation is not acceptable when supporting > features such as suspend or kexec. As the Versatile platforms are > ARM development platforms which do not have suspend support, this is > acceptable there, but not for production hardware. > > None of these three facilities/implementations should be used on > modern production hardware, yet we have a number of copies of this > code. > > This series addresses that by removing the inappropriate copies of > some Realview/Versatile Express specific workarounds, and makes it > (hopefully) more clear that introducing this code is really not > acceptable. > > To discourage copying the Versatile code, further comments are added > and the functions renamed for CPU hotplug to be "immitation" to make > it clear that it's not a real implementation. > > We tried reducing the duplication in the past with ideas around > consolidating the pen_release/boot_lock/immitation hotplug stuff, > but I nacked that because it's not an acceptable implementation for > production hardware. However, we did decide to consolidate the > "pen_release" definition. In hind sight, that was a mistake, > because that gave more credence to that way of doing things, and > also gave rise to buggy implementations which only read from that > variable - meaning it served no useful purpose. > > There are some rather complex cases that remain, and those need the > SoC folk to fix. > > I have left the Actions Semi patch in place since following patches > depend on it, but there is a five-patch series from Linus Walleij > that address this platform which should replace this patch - with > the patch concerned marked as "RFT" - request for testing. > > arch/arm/include/asm/smp.h | 1 - > arch/arm/kernel/smp.c | 6 -- > arch/arm/mach-actions/platsmp.c | 15 --- > arch/arm/mach-exynos/headsmp.S | 2 +- > arch/arm/mach-exynos/platsmp.c | 31 +++--- > arch/arm/mach-omap2/omap-smp.c | 20 ---- > arch/arm/mach-oxnas/Makefile | 1 - > arch/arm/mach-oxnas/hotplug.c | 109 -------------------- > arch/arm/mach-oxnas/platsmp.c | 4 - > arch/arm/mach-prima2/common.h | 2 + > arch/arm/mach-prima2/headsmp.S | 2 +- > arch/arm/mach-prima2/hotplug.c | 3 +- > arch/arm/mach-prima2/platsmp.c | 17 ++-- > arch/arm/mach-qcom/platsmp.c | 26 ----- > arch/arm/mach-realview/Makefile | 1 - > arch/arm/mach-realview/hotplug.c | 111 --------------------- > arch/arm/mach-realview/hotplug.h | 1 - > arch/arm/mach-realview/platsmp-dt.c | 8 +- > arch/arm/mach-spear/generic.h | 2 + > arch/arm/mach-spear/headsmp.S | 2 +- > arch/arm/mach-spear/hotplug.c | 4 +- > arch/arm/mach-spear/platsmp.c | 27 +++-- > arch/arm/mach-sti/Makefile | 2 +- > arch/arm/mach-sti/headsmp.S | 43 -------- > arch/arm/mach-sti/platsmp.c | 62 +----------- > arch/arm/mach-vexpress/Makefile | 1 - > arch/arm/mach-vexpress/core.h | 2 - > arch/arm/mach-vexpress/platsmp.c | 7 ++ > arch/arm/plat-versatile/Makefile | 1 + > arch/arm/plat-versatile/headsmp.S | 2 +- > .../{mach-vexpress => plat-versatile}/hotplug.c | 47 ++++----- > arch/arm/plat-versatile/include/plat/platsmp.h | 2 + > arch/arm/plat-versatile/platsmp.c | 47 ++++++--- > 33 files changed, 132 insertions(+), 479 deletions(-) > delete mode 100644 arch/arm/mach-oxnas/hotplug.c > delete mode 100644 arch/arm/mach-realview/hotplug.c > delete mode 100644 arch/arm/mach-realview/hotplug.h > delete mode 100644 arch/arm/mach-sti/headsmp.S > rename arch/arm/{mach-vexpress => plat-versatile}/hotplug.c (56%) > > -- > RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up > According to speedtest.net: 11.9Mbps down 500kbps up > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel