edce21216a
So the reserve_ebda_region() code has accumulated a number of problems over the years that make it really difficult to read and understand: - The calculation of 'lowmem' and 'ebda_addr' is an unnecessarily interleaved mess of first lowmem, then ebda_addr, then lowmem tweaks... - 'lowmem' here means 'super low mem' - i.e. 16-bit addressable memory. In other parts of the x86 code 'lowmem' means 32-bit addressable memory... This makes it super confusing to read. - It does not help at all that we have various memory range markers, half of which are 'start of range', half of which are 'end of range' - but this crucial property is not obvious in the naming at all ... gave me a headache trying to understand all this. - Also, the 'ebda_addr' name sucks: it highlights that it's an address (which is obvious, all values here are addresses!), while it does not highlight that it's the _start_ of the EBDA region ... - 'BIOS_LOWMEM_KILOBYTES' says a lot of things, except that this is the only value that is a pointer to a value, not a memory range address! - The function name itself is a misnomer: it says 'reserve_ebda_region()' while its main purpose is to reserve all the firmware ROM typically between 640K and 1MB, while the 'EBDA' part is only a small part of that ... - Likewise, the paravirt quirk flag name 'ebda_search' is misleading as well: this too should be about whether to reserve firmware areas in the paravirt case. - In fact thinking about this as 'end of RAM' is confusing: what this function *really* wants to reserve is firmware data and code areas! Once the thinking is inverted from a mixed 'ram' and 'reserved firmware area' notion to a pure 'reserved area' notion everything becomes a lot clearer. To improve all this rewrite the whole code (without changing the logic): - Firstly invert the naming from 'lowmem end' to 'BIOS reserved area start' and propagate this concept through all the variable names and constants. BIOS_RAM_SIZE_KB_PTR // was: BIOS_LOWMEM_KILOBYTES BIOS_START_MIN // was: INSANE_CUTOFF ebda_start // was: ebda_addr bios_start // was: lowmem BIOS_START_MAX // was: LOWMEM_CAP - Then clean up the name of the function itself by renaming it to reserve_bios_regions() and renaming the ::ebda_search paravirt flag to ::reserve_bios_regions. - Fix up all the comments (fix typos), harmonize and simplify their formulation and remove comments that become unnecessary due to the much better naming all around. Signed-off-by: Ingo Molnar <mingo@kernel.org>
36 lines
797 B
C
36 lines
797 B
C
#include <linux/kernel.h>
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#include <linux/init.h>
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#include <asm/setup.h>
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#include <asm/bios_ebda.h>
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void __init x86_early_init_platform_quirks(void)
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{
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x86_platform.legacy.rtc = 1;
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x86_platform.legacy.reserve_bios_regions = 0;
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x86_platform.legacy.devices.pnpbios = 1;
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switch (boot_params.hdr.hardware_subarch) {
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case X86_SUBARCH_PC:
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x86_platform.legacy.reserve_bios_regions = 1;
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break;
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case X86_SUBARCH_XEN:
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case X86_SUBARCH_LGUEST:
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case X86_SUBARCH_INTEL_MID:
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case X86_SUBARCH_CE4100:
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x86_platform.legacy.devices.pnpbios = 0;
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x86_platform.legacy.rtc = 0;
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break;
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}
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if (x86_platform.set_legacy_features)
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x86_platform.set_legacy_features();
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}
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#if defined(CONFIG_PNPBIOS)
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bool __init arch_pnpbios_disabled(void)
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{
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return x86_platform.legacy.devices.pnpbios == 0;
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}
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#endif
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