From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5B0FC761AF; Thu, 30 Mar 2023 08:12:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229901AbjC3IMx (ORCPT + 1 other); Thu, 30 Mar 2023 04:12:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229987AbjC3IMp (ORCPT ); Thu, 30 Mar 2023 04:12:45 -0400 Received: from mail-yw1-x1133.google.com (mail-yw1-x1133.google.com [IPv6:2607:f8b0:4864:20::1133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C206D76B0 for ; Thu, 30 Mar 2023 01:12:14 -0700 (PDT) Received: by mail-yw1-x1133.google.com with SMTP id 00721157ae682-536af432ee5so341331757b3.0 for ; Thu, 30 Mar 2023 01:12:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1680163931; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=LQCYgbZHrv29At0jbIiZAbPjoR2bcYIsz7/d6inu7f8=; b=ExPqwkg7v1NJaAb/s/k5m0AsXdPeqWANvICm34UN83+g91kLHVNxTL6wIK95elgwZ0 BsoWOOEBJNZZMuzO0jd9e5ZnX+piu95PYHJc8aCAeb74EZLSXYYZcUnjlcrwcSx9uUSn +ZylXYodLpHskZhPbl4FteqkYPSevcOTC9viahsIQVrxIIJjVrJEKuNvoC6mbX+9pqR3 89vqEOP7c1GfiVA/eOXrKlUJ2J9zGfYuC7KwccmlIyO2J0GIlDQpCElJBkH4Lwj1h0sT ooCHH5PYBMyLFmPU8W7WigILMi6/95wflgUZh1w0ygoWmHzMdYahkSPYjw44g9lyJXD6 gNjA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680163931; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=LQCYgbZHrv29At0jbIiZAbPjoR2bcYIsz7/d6inu7f8=; b=BFdHizwSvxNQ1hRAne1Hzk+pV577EAIjpAqCK53+dWIJ4axLVEqwtIKpWdY/xBGo0f Xs/PIuEcuE6XIPgfVhFpz/OO2Pr5bz/fvHzFLihDKYptElloca7zYp60iFAxFTaDtbmG jGLhuYsIMRCjCw7b0SzVdp3gjhmz3/EdYBeHQWPSZEWbLH8zy4QE2EW/eKUI6dLDneZr wNpbBQwgo4qprgvJwFWaKvmG+BxJW1vnknDRNDFgTIDAwZgsYz1rSYWI6gn33GlGDlZy ico8GrBEYpwqJyygOlzIVrPFpRPloezZRaAh51J7BmOYksQQT9VJRUUr0QWJSbTLwpHO 8gbw== X-Gm-Message-State: AAQBX9eCBGYWz0b/8MM9Hb6hVMpb9aEEim4K/y9hYQUnYeew2ljjDw73 Jh3cqBvzx2zlFuYm0d6wRl/70wDInVMv1/9sEH7S7g== X-Google-Smtp-Source: AKy350a/1aBIXwj5sRzvro+POKQZrQ8u1qzHA9lYRVf8cH3+kLmmcEZ591QzYhrOYx7KtYdusctEvAjdnpZqGPXhdtA= X-Received: by 2002:a81:c84a:0:b0:541:753d:32f9 with SMTP id k10-20020a81c84a000000b00541753d32f9mr10995359ywl.9.1680163931243; Thu, 30 Mar 2023 01:12:11 -0700 (PDT) MIME-Version: 1.0 References: <20230327121317.4081816-1-arnd@kernel.org> <20230327121317.4081816-19-arnd@kernel.org> In-Reply-To: <20230327121317.4081816-19-arnd@kernel.org> From: Linus Walleij Date: Thu, 30 Mar 2023 10:12:00 +0200 Message-ID: Subject: Re: [PATCH 18/21] ARM: drop SMP support for ARM11MPCore To: Arnd Bergmann Cc: linux-kernel@vger.kernel.org, Arnd Bergmann , Vineet Gupta , Russell King , Neil Armstrong , Catalin Marinas , Will Deacon , Guo Ren , Brian Cain , Geert Uytterhoeven , Michal Simek , Thomas Bogendoerfer , Dinh Nguyen , Stafford Horne , Helge Deller , Michael Ellerman , Christophe Leroy , Paul Walmsley , Palmer Dabbelt , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Max Filippov , Christoph Hellwig , Robin Murphy , Lad Prabhakar , Conor Dooley , linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-oxnas@groups.io, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, Daniel Golle Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-openrisc@vger.kernel.org On Mon, Mar 27, 2023 at 2:16=E2=80=AFPM Arnd Bergmann wro= te: > From: Arnd Bergmann > > The cache management operations for noncoherent DMA on ARMv6 work > in two different ways: > > * When CONFIG_DMA_CACHE_RWFO is set, speculative prefetches on in-flight > DMA buffers lead to data corruption when the prefetched data is writte= n > back on top of data from the device. > > * When CONFIG_DMA_CACHE_RWFO is disabled, a cache flush on one CPU > is not seen by the other core(s), leading to inconsistent contents > accross the system. > > As a consequence, neither configuration is actually safe to use in a > general-purpose kernel that is used on both MPCore systems and ARM1176 > with prefetching enabled. > > We could add further workarounds to make the behavior more dynamic based > on the system, but realistically, there are close to zero remaining > users on any ARM11MPCore anyway, and nobody seems too interested in it, > compared to the more popular ARM1176 used in BMC2835 and AST2500. > > The Oxnas platform has some minimal support in OpenWRT, but most of the > drivers and dts files never made it into the mainline kernel, while the > Arm Versatile/Realview platform mainly serves as a reference system but > is not necessary to be kept working once all other ARM11MPCore are gone. > > 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. > > Cc: Neil Armstrong > Cc: Daniel Golle > Cc: Linus Walleij > Cc: linux-oxnas@groups.io > Signed-off-by: Arnd Bergmann Yeah, we discussed this earlier, let's just drop it. Not worth the effort. Acked-by: Linus Walleij Yours, Linus Walleij