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a4dff76924
There isn't an explicit stolen memory base register on gen2. Some old comment in the i915 code suggests we should get it via max_low_pfn_mapped, but that's clearly a bad idea on my MGM. The e820 map in said machine looks like this: BIOS-e820: [mem 0x0000000000000000-0x000000000009f7ff] usable BIOS-e820: [mem 0x000000000009f800-0x000000000009ffff] reserved BIOS-e820: [mem 0x00000000000ce000-0x00000000000cffff] reserved BIOS-e820: [mem 0x00000000000dc000-0x00000000000fffff] reserved BIOS-e820: [mem 0x0000000000100000-0x000000001f6effff] usable BIOS-e820: [mem 0x000000001f6f0000-0x000000001f6f7fff] ACPI data BIOS-e820: [mem 0x000000001f6f8000-0x000000001f6fffff] ACPI NVS BIOS-e820: [mem 0x000000001f700000-0x000000001fffffff] reserved BIOS-e820: [mem 0x00000000fec10000-0x00000000fec1ffff] reserved BIOS-e820: [mem 0x00000000ffb00000-0x00000000ffbfffff] reserved BIOS-e820: [mem 0x00000000fff00000-0x00000000ffffffff] reserved That makes max_low_pfn_mapped = 1f6f0000, so assuming our stolen memory would start there would place it on top of some ACPI memory regions. So not a good idea as already stated. The 9MB region after the ACPI regions at 0x1f700000 however looks promising given that the macine reports the stolen memory size to be 8MB. Looking at the PGTBL_CTL register, the GTT entries are at offset 0x1fee00000, and given that the GTT entries occupy 128KB, it looks like the stolen memory could start at 0x1f700000 and the GTT entries would occupy the last 128KB of the stolen memory. After some more digging through chipset documentation, I've determined the BIOS first allocates space for something called TSEG (something to do with SMM) from the top of memory, and then it allocates the graphics stolen memory below that. Accordind to the chipset documentation TSEG has a fixed size of 1MB on 855. So that explains the top 1MB in the e820 region. And it also confirms that the GTT entries are in fact at the end of the the stolen memory region. Derive the stolen memory base address on gen2 the same as the BIOS does (TOM-TSEG_SIZE-stolen_size). There are a few differences between the registers on various gen2 chipsets, so a few different codepaths are required. 865G is again bit more special since it seems to support enough memory to hit 4GB address space issues. This means the PCI allocations will also affect the location of the stolen memory. Fortunately there appears to be the TOUD register which may give us the correct answer directly. But the chipset docs are a bit unclear, so I'm not 100% sure that the graphics stolen memory is always the last thing the BIOS steals. Someone would need to verify it on a real system. I tested this on the my 830 and 855 machines, and so far everything looks peachy. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Link: http://lkml.kernel.org/r/1391628540-23072-3-git-send-email-ville.syrjala@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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