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x86/PCI: Add "pci=big_root_window" option for AMD 64-bit windows

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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
it.

Signed-off-by: Christian König <christian.koenig@amd.com>
[bhelgaas: changelog, extend doc, mention taint in dmesg]
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>
This commit is contained in:
=?UTF-8?q?Christian=20K=C3=B6nig?= 2018-01-11 14:23:29 +01:00 • committed by Bjorn Helgaas
parent 1291a0d504
commit f32ab75471
4 changed files with 18 additions and 1 deletions
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6
Documentation/admin-guide/kernel-parameters.txt
View file

@ -3094,6 +3094,12 @@
pcie_scan_all Scan all possible PCIe devices. Otherwise we
only look for one device below a PCIe downstream
port.
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
Management.