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Fri, 31 Mar 2023 08:54:47 -0400 (EDT) Received: from imap51 ([10.202.2.101]) by compute6.internal (MEProxy); Fri, 31 Mar 2023 08:54:47 -0400 X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrvdeiuddgheegucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepofgfggfkjghffffhvfevufgtsehttdertderredtnecuhfhrohhmpedftehr nhguuceuvghrghhmrghnnhdfuceorghrnhgusehkvghrnhgvlhdrohhrgheqnecuggftrf grthhtvghrnhepvdeviefgtedugeevieelvdfgveeuvdfgteegfeeiieejjeffgeeghedu gedtveehnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomh eprghrnhguodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdduvdekhedujedt vdegqddvkeejtddtvdeigedqrghrnhgupeepkhgvrhhnvghlrdhorhhgsegrrhhnuggsrd guvg X-ME-Proxy: Feedback-ID: i36794607:Fastmail Received: by mailuser.nyi.internal (Postfix, from userid 501) id 447D4B60089; Fri, 31 Mar 2023 08:54:47 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-238-g746678b8b6-fm-20230329.001-g746678b8 Mime-Version: 1.0 Message-Id: <50776011-53a5-4823-8c41-d2b96a828199@app.fastmail.com> In-Reply-To: References: <20230327121317.4081816-1-arnd@kernel.org> <20230327121317.4081816-19-arnd@kernel.org> Date: Fri, 31 Mar 2023 14:54:27 +0200 From: "Arnd Bergmann" To: "Joel Stanley" Cc: linux-arm-kernel@lists.infradead.org, "Andrew Jeffery" Subject: Re: [PATCH 18/21] ARM: drop SMP support for ARM11MPCore X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230331_055453_221765_349C1C5D X-CRM114-Status: GOOD ( 18.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Mar 30, 2023, at 13:28, Joel Stanley wrote: > On Mon, 27 Mar 2023 at 12:18, Arnd Bergmann wrote: > >> Take the easy way out here and drop support for multiprocessing on >> ARMv6, along with the CONFIG_DMA_CACHE_RWFO option and the cache >> management implementation for it. This also helps with other ARMv6 >> issues, but for the moment leaves the ability to build a kernel that >> can run on both ARMv7 SMP and single-processor ARMv6, which we probably >> want to stop supporting as well, but not as part of this series. > > Why's that? I currently build a kernel for the ast2600 (dual core > cortex a7) and ast2500 (arm1176). There are actually three generations of ARMv6: - "armv6" arm1136r0, in practice only omap2 and i.mx31 - "armv6k" arm1136r1 and arm1176, common in ast2500, bcm2835, i.mx35, and s3c64xx - "armv6k" arm11mpcore in oxnas and realview The early armv6 ones are halfway between armv5 and armv6k, which causes a number of problems: - cannot use 8-bit and 16-bit sub-word atomics (strexh etc) and double-word atomics (strexd) that may be needed by some drivers - need to use cp15 barriers instead of isb/dsb etc, which breaks compatibility with armv8 hardware in a multiplatform kernel - missing TLS register requires horrid workarounds for CURRENT_POINTER_IN_TPIDRURO. - Running an SMP-enabled kernel on armv6 requires SMP_ON_UP (this is also required for at least one ARMv7 SoC) One idea that we have discussed as a long-term solution for all of the above would be to change support for armv6 from being compatible with armv7 to being compatible with armv5. arm11mpcore is currently tied to armv7 because of SMP support, but once we drop SMP support for it, we have more freedom and can move armv6 and armv6k uniprocessor support together with armv5. I already did an initial patch last year, but it needs more work to ensure that it correctly addresses everything that currently assumes that armv6 cannot coexist with older cores in the same kernel. If this works out, we'll be able to have a combined ast2400/ ast2500/omap1/omap2/imx2/imx3 kernel separate from ast2600/ omap3/imx5, but hopefully not more kernels that anyone needs to test. For Debian, this would allow armel to ship a combined kernel for Raspberry Pi and the ARMv5 parts in place of the two separate kernels it currently has, but it's not clear there will actually be another Debian armel release after Bookworm. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel