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From: Ash Logan Subject: 32-bit HIGHMEM and game console downstreams Content-Language: en-US To: arnd@arndb.de, christophe.leroy@csgroup.eu Cc: "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" , officialTechflashYT@gmail.com, AWilcox@Wilcox-Tech.com, Michael Ellerman Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hello! LWN recently did a piece on 32-bit support in the kernel, and thought as a user of 32-bit I would share my 2c. [1] I maintain a downstream fork of 6.6 to support the Nintendo Wii U hardware [2]. I'm also in regular contact with another doing the same for the older Wii [3]. Linux on this era of game consoles is doing pretty well :) The Wii and Wii U are both 32-bit PowerPC machines with holes in their memory map, which I think makes them interesting for this discussion. Let me summarize the hardware and kernels involved: Wii (2006) - 1x PowerPC 750CL "Broadway" @ 729MHz - 24MB "MEM1" + 64MB "MEM2" (non-contiguous - MEM2 starts 256MiB in) - Kernel 4.19 (+ CIP patchset), dev has been working on forward-porting all the drivers one major version at a time (he's currently up to 5.15 last I checked) + limited upstream support (hardware bringup, UART, not many peripherals) Wii U (2012) - 3x PowerPC 750CL "Espresso" @ 1.2GHz - 32MB "MEM1" + 2GB "MEM2" (also starts 256MiB in) + various small SRAMs - Kernel 6.6 (+ LTS patchset), I also had a run at upstreaming some of it in 2022 [4] and would eventually like to go again Special mention to the GameCube, basically a slower Wii with only 24MB direct RAM and 16MB of non-mapped "ARAM". Wii Linux has experimental support for this where they use the ARAM as swap. All of these are flatmem devices, as that's all the 32-bit PowerPC arch supports, with the Wii U additionally enabling highmem for its 2GB of RAM. Both devices have a small memory area (MEM1) with the "bulk" of RAM starting at 256MiB. The Wii U in particular sounds like a candidate system for densemem - I would like to read up more about this if I can, I was only able to find seemingly unrelated information about CXL when searching online. There is a somewhat active userbase for both devices. I only have stats for the Wii U side, but some rough nginx grepping for the last few days - Sep 7th-Sep 12th - shows 39 downloads of distribution tarballs and bootloader binaries in that period, not including torrents. In the past 2 weeks - Aug 29th-Sep 12th - 9 people joined the community Discord, 442 total. Anecdotally, the Wii Linux userbase appears at least twice as big (based on their Discord activity). Distribution-wise, we're supported by ArchPOWER [5], Adélie Linux [6], and other distros. The Wii U's Espresso has CPU errata requiring a patched compiler, and both distributions ship separate package repos for this CPU. ArchPOWER requested I rebase onto 6.6 so they could have firmware compression - previously the Wii U was on 4.19 - so there is some demand for newer kernel features as well. I know I'm talking about hobbyist use - and mostly downstream use at that - and I do suspect that in the event of a wider 32-bit deprecation we'd be fine on the final LTS, whatever that ends up being. Still, I think the Wii and Wii U represent a decent number of 32-bit users, so I wanted to add to the conversation here. Thanks, Ash [1] https://lwn.net/Articles/1035727/ [2] https://linux-wiiu.org/ [3] https://wii-linux.org/ [4] https://lore.kernel.org/lkml/20221119113041.284419-1-ash@heyquark.com/ [5] https://archlinuxpower.org/ [6] https://www.adelielinux.org/