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// SPDX-License-Identifier: GPL-2.0
#include <linux/dmi.h>
#include <linux/ioport.h>
#include <asm/e820/api.h>
static void resource_clip(struct resource *res, resource_size_t start,
resource_size_t end)
{
resource_size_t low = 0, high = 0;
if (res->end < start || res->start > end)
return; /* no conflict */
if (res->start < start)
low = start - res->start;
if (res->end > end)
high = res->end - end;
/* Keep the area above or below the conflict, whichever is larger */
if (low > high)
res->end = start - 1;
else
res->start = end + 1;
}
/*
* Some BIOS-es contain a bug where they add addresses which map to
* system RAM in the PCI host bridge window returned by the ACPI _CRS
* method, see commit 4dc2287c1805 ("x86: avoid E820 regions when
* allocating address space"). To avoid this Linux by default excludes
* E820 reservations when allocating addresses since 2010.
* In 2019 some systems have shown-up with E820 reservations which cover
* the entire _CRS returned PCI host bridge window, causing all attempts
* to assign memory to PCI BARs to fail if Linux uses E820 reservations.
*
* Ideally Linux would fully stop using E820 reservations, but then
* the old systems this was added for will regress.
* Instead keep the old behavior for old systems, while ignoring the
* E820 reservations for any systems from now on.
*/
static void remove_e820_regions(struct resource *avail)
{
int i, year = dmi_get_bios_year();
struct e820_entry *entry;
if (year >= 2018)
return;
pr_info_once("PCI: Removing E820 reservations from host bridge windows\n");
for (i = 0; i < e820_table->nr_entries; i++) {
entry = &e820_table->entries[i];
resource_clip(avail, entry->addr,
entry->addr + entry->size - 1);
}
}
void arch_remove_reservations(struct resource *avail)
{
/*
* Trim out BIOS area (high 2MB) and E820 regions. We do not remove
* the low 1MB unconditionally, as this area is needed for some ISA
* cards requiring a memory range, e.g. the i82365 PCMCIA controller.
*/
if (avail->flags & IORESOURCE_MEM) {
resource_clip(avail, BIOS_ROM_BASE, BIOS_ROM_END);
remove_e820_regions(avail);
}
}
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