Commit f32ab754 authored by =?UTF-8?q?Christian=20K=C3=B6nig?='s avatar =?UTF-8?q?Christian=20K=C3=B6nig?= Committed by Bjorn Helgaas
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x86/PCI: Add "pci=big_root_window" option for AMD 64-bit windows

Only try to enable a 64-bit window on AMD CPUs when "pci=big_root_window"
is specified.

This taints the kernel because the new 64-bit window uses address space we
don't know anything about, and it may contain unreported devices or memory
that would conflict with the window.

The pci_amd_enable_64bit_bar() quirk that enables the window is specific to
AMD CPUs.  The generic solution would be to have the firmware enable the
window and describe it in the host bridge's _CRS method, or at least
describe it in the _PRS method so the OS would have the option of enabling
Signed-off-by: default avatarChristian König <>
[bhelgaas: changelog, extend doc, mention taint in dmesg]
Signed-off-by: default avatarBjorn Helgaas <>
parent 1291a0d5
......@@ -3094,6 +3094,12 @@
pcie_scan_all Scan all possible PCIe devices. Otherwise we
only look for one device below a PCIe downstream
big_root_window Try to add a big 64bit memory window to the PCIe
root complex on AMD CPUs. Some GFX hardware
can resize a BAR to allow access to all VRAM.
Adding the window is slightly risky (it may
conflict with unreported devices), so this
taints the kernel.
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
......@@ -38,6 +38,7 @@ do { \
#define PCI_NOASSIGN_ROMS 0x80000
#define PCI_ROOT_NO_CRS 0x100000
#define PCI_NOASSIGN_BARS 0x200000
#define PCI_BIG_ROOT_WINDOW 0x400000
extern unsigned int pci_probe;
extern unsigned long pirq_table_addr;
......@@ -594,6 +594,11 @@ char *__init pcibios_setup(char *str)
} else if (!strcmp(str, "nocrs")) {
pci_probe |= PCI_ROOT_NO_CRS;
return NULL;
} else if (!strcmp(str, "big_root_window")) {
pci_probe |= PCI_BIG_ROOT_WINDOW;
return NULL;
} else if (!strcmp(str, "earlydump")) {
pci_early_dump_regs = 1;
return NULL;
......@@ -667,6 +667,9 @@ static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
struct resource *res, *conflict;
struct pci_dev *other;
if (!(pci_probe & PCI_BIG_ROOT_WINDOW))
/* Check that we are the only device of that type */
other = pci_get_device(dev->vendor, dev->device, NULL);
if (other != dev ||
......@@ -714,7 +717,9 @@ static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
res->start = conflict->end + 1;
dev_info(&dev->dev, "adding root bus resource %pR\n", res);
dev_info(&dev->dev, "adding root bus resource %pR (tainting kernel)\n",
base = ((res->start >> 8) & AMD_141b_MMIO_BASE_MMIOBASE_MASK) |
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