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Thu, 30 Mar 2023 09:40:43 -0700 (PDT) Received: from [172.20.10.2] ([37.166.66.243]) by smtp.gmail.com with ESMTPSA id w20-20020a05600c475400b003f034c76e85sm3545852wmo.38.2023.03.30.09.40.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Mar 2023 09:40:43 -0700 (PDT) Message-ID: Date: Thu, 30 Mar 2023 18:40:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH 18/21] ARM: drop SMP support for ARM11MPCore Content-Language: en-GB To: Arnd Bergmann , Arnd Bergmann , linux-kernel@vger.kernel.org References: <20230327121317.4081816-1-arnd@kernel.org> <20230327121317.4081816-19-arnd@kernel.org> <6a5bd3a3-87e0-4a24-89ca-d265b0817a95@app.fastmail.com> From: Neil Armstrong In-Reply-To: <6a5bd3a3-87e0-4a24-89ca-d265b0817a95@app.fastmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Fri, 31 Mar 2023 10:07:14 +1100 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Rich Felker , linux-sh@vger.kernel.org, Catalin Marinas , Linus Walleij , John Paul Adrian Glaubitz , Daniel Golle , Max Filippov , "Conor.Dooley" , guoren , "linux-csky@vger.kernel.org" , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Will Deacon , Christoph Hellwig , Helge Deller , Russell King , Geert Uytterhoeven , Vineet Gupta , linux-snps-arc@lists.infradead.org, linux-xtensa@linux-xtensa.org, "Lad, Prabhakar" , linux-m68k@lists.linux-m68k.org, Paul Walmsley , Stafford Horne , linux-arm-kernel@lists.infradead.org, Brian Cain , Michal Simek , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, "linux-openrisc@vger.kernel.org" , linuxppc-dev@lists.ozlabs.org, linux-mips@vger.kernel.org, Dinh Nguyen , Palmer Dabbelt , linux-hexagon@vger.kernel.org, "linux-oxnas@groups.io" , Robin Murphy , "David S . Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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