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71 lines
2.2 KiB
71 lines
2.2 KiB
#include <linux/kernel.h> |
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#include <linux/init.h> |
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#include <linux/memblock.h> |
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#include <asm/setup.h> |
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#include <asm/bios_ebda.h> |
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/* |
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* The BIOS places the EBDA/XBDA at the top of conventional |
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* memory, and usually decreases the reported amount of |
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* conventional memory (int 0x12) too. This also contains a |
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* workaround for Dell systems that neglect to reserve EBDA. |
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* The same workaround also avoids a problem with the AMD768MPX |
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* chipset: reserve a page before VGA to prevent PCI prefetch |
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* into it (errata #56). Usually the page is reserved anyways, |
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* unless you have no PS/2 mouse plugged in. |
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* |
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* This functions is deliberately very conservative. Losing |
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* memory in the bottom megabyte is rarely a problem, as long |
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* as we have enough memory to install the trampoline. Using |
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* memory that is in use by the BIOS or by some DMA device |
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* the BIOS didn't shut down *is* a big problem. |
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*/ |
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#define BIOS_LOWMEM_KILOBYTES 0x413 |
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#define LOWMEM_CAP 0x9f000U /* Absolute maximum */ |
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#define INSANE_CUTOFF 0x20000U /* Less than this = insane */ |
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void __init reserve_ebda_region(void) |
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{ |
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unsigned int lowmem, ebda_addr; |
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/* |
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* To determine the position of the EBDA and the |
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* end of conventional memory, we need to look at |
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* the BIOS data area. In a paravirtual environment |
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* that area is absent. We'll just have to assume |
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* that the paravirt case can handle memory setup |
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* correctly, without our help. |
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*/ |
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if (paravirt_enabled()) |
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return; |
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/* end of low (conventional) memory */ |
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lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES); |
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lowmem <<= 10; |
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/* start of EBDA area */ |
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ebda_addr = get_bios_ebda(); |
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/* |
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* Note: some old Dells seem to need 4k EBDA without |
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* reporting so, so just consider the memory above 0x9f000 |
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* to be off limits (bugzilla 2990). |
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*/ |
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/* If the EBDA address is below 128K, assume it is bogus */ |
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if (ebda_addr < INSANE_CUTOFF) |
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ebda_addr = LOWMEM_CAP; |
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/* If lowmem is less than 128K, assume it is bogus */ |
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if (lowmem < INSANE_CUTOFF) |
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lowmem = LOWMEM_CAP; |
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/* Use the lower of the lowmem and EBDA markers as the cutoff */ |
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lowmem = min(lowmem, ebda_addr); |
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lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */ |
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/* reserve all memory between lowmem and the 1MB mark */ |
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memblock_reserve(lowmem, 0x100000 - lowmem); |
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}
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