[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH ARM v6 00/14] mini-os: initial ARM support
On 17 July 2014 16:55, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: > On Wed, 2014-07-16 at 22:29 +0100, Julien Grall wrote: > >> > There are two assumptions the code makes that may need changing in the >> > future, but >> > which hopefully don't need to hold up this initial support: >> > >> > - The assumption that the kernel will be loaded at start of RAM + 0x8000. >> > >> > - The assumption that Xen will mark the GIC address range as device memory. >> > This should probably be fixed when the C code gains the ability to >> > control >> > the translation tables, map 4K pages, etc. >> >> I'm fine with the assumptions for an initial support. Did you write-down >> somewhere those restrictions? So if an issue happen in the future, we >> will be able to find quickly the issue. > > Yeah. we can live with them for now, I think. It should be documented > though. I've noted the offset requirement in the linker script and the GIC memory type assumption in a comment in gic.c. > What sort of time line are you foreseeing for fixing them, in terms of > before or after 4.5? If the GIC will always occupy a distinct set of 1MB sections then flagging those is easy enough. Otherwise, we'd have to add support for the second-level page tables, which would complicate things a little. Making the boot code work from arbitrary offsets looks very difficult. I guess we'd need to compile libfdt as PIC, set up a temporary C stack after the kernel (we can assume there's some RAM following it I think), parse the FDT to find the base address, copy the kernel forwards or backwards word by word (first copying the copying code to a safe location somewhere). It all seems very inefficient. From my point of view, it would seem better to have some way to specify the desired load offset. > We should probably consider sticking a "tech preview" or similar label > on mini-os/ARM in 4.5 if these issues remain (the load address one in > particular). -- Dr Thomas Leonard http://0install.net/ GPG: 9242 9807 C985 3C07 44A6 8B9A AE07 8280 59A5 3CC1 GPG: DA98 25AE CAD0 8975 7CDA BD8E 0713 3F96 CA74 D8BA _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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