Messages in this thread | | | From | ron minnich <> | Date | Thu, 16 Apr 2020 07:55:01 -0700 | Subject | Re: [PATCH] mtd: parsers: Support '[]' for id in mtdparts |
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On Thu, Apr 16, 2020 at 2:51 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> I suppose the use case is using PCI-based MTD devices for testing > something android images on desktops? I'm surprised it didn't > come up earlier.
Thanks. In this case it's for systems that companies are deploying into their data centers, using linuxboot (linuxboot.org) and Intel chipsets. On Intel chipsets, there is a 64 MiB SPI part, but only 16 MiB is directly addressable.
Linux goes in the memory-addressable part of the SPI, and UEFI loads it into RAM, since to UEFI the kernel is just another UEFI driver -- in fact in most cases we replace the UEFI shell with Linux.
But we need a file system, and with the huge amount of drivers that come with UEFI there's not much room in the top 16M. (we're working to fix that glitch, a process we call DXE-ectomy, but it takes time).
We wish to place a file system in the low 48 MiB -- lots of room there.
So what one can do is put a squashfs-formatted file system in that low part of SPI, and, using this mtdparts capability, point the kernel at it ("root=/dev/mtd1 mtdparts=[a:b.c]etc.etc"). It's a lifesaver for those of us using u-root for our userland.
ron
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