From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Armstrong Subject: Re: [PATCH 18/21] ARM: drop SMP support for ARM11MPCore Date: Thu, 30 Mar 2023 18:40:39 +0200 Message-ID: References: <20230327121317.4081816-1-arnd@kernel.org> <20230327121317.4081816-19-arnd@kernel.org> <6a5bd3a3-87e0-4a24-89ca-d265b0817a95@app.fastmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1680194444; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=kz/2H/BTIuKLAKXpo3BrU6LM5Cbhbn/nr7Y/43JgHBo=; b=ZlHh9rnbOioBf3nV/3JYjFE5Qh/bXo4StWdfNEsfuVogmTWridktEfoOhrvWpVNNhE 0z/X0MYaJjK/QYT4ITLVIUdplXX/DuXksJC0IpeVKtHOrPLMJe9eSvHXtK4aOFvf4tZs /AbEoXyA7m4P/L9dHHblxxWiEqpMvlOY5GomHTzf+A7mUydBq8mvV4Xac+jQ3DUw+m7d M7bxCvgbaGFMHEPdtiAa6ky4qk4LVn0KlYFTszccyx+U9QZE1gLR26fPAJN9gaLHkJpX WQORjeI04LW5T5Q3kvDg17MPl5M4+c/QRypn5gBwOkQH/rvgvQ4KM27LU9sBhn9IdM+7 8UVg== Content-Language: en-GB In-Reply-To: <6a5bd3a3-87e0-4a24-89ca-d265b0817a95@app.fastmail.com> List-ID: Content-Type: text/plain; charset="utf-8"; format="flowed" To: Arnd Bergmann , Arnd Bergmann , linux-kernel@vger.kernel.org Cc: Vineet Gupta , Russell King , Linus Walleij , Catalin Marinas , Will Deacon , guoren , 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" Le 30/03/2023 à 12:03, Arnd Bergmann a écrit : > On Thu, Mar 30, 2023, at 09:48, Neil Armstrong wrote: >> On 27/03/2023 14:13, Arnd Bergmann wrote: >>> 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 written >>> 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. >> >> Acked-by: Neil Armstrong >> >> It's sad but it's the reality, there's no chance full OXNAS support will >> ever come upstream and no real work has been done for years. >> >> I think OXNAS support can be programmed for removal for next release, >> it would need significant work to rework current support to make it acceptable >> before trying to upstream missing bits anyway. > > Ok, thanks for your reply! > > To clarify, do you think we should plan for removal after the next > stable release (6.3, removed in 6.4), or after the next LTS > release (probably 6.6, removed in 6.7)? As far as I understand, > the next OpenWRT release (23.x) will be based on linux-5.15, > and the one after that (24.x) would likely still use 6.1, unless > they skip an LTS kernel. I think it's ok to remove it ASAP, or at least before the next LTS, not having SMP makes the platform barely usable so the earliest is the best. Neil > > Arnd