Firmware Test Suite - crs test

The _CRS test checks to see if the kernel is configuring PCI host bridge windows using the appropriate ACPI object _CRS (Current Resource Settings). For more information on _CRS see section 6.2.2 of the ACPI reference and also arch/x86/pci/acpi.c in the kernel for the PCI host bridge configuration.

Please note:

  • The test will skipped if the machine was booted with kernel option"pci=nocrs" because the kernel was told to explicitly ignore host bridge windows _CRS settings.

The test will fail if:

  • The kernel cannot determine the BIOS age, so it has to assume the the BIOS is too old to correctly specify the host bridge MMIO aperture using _CRS. One can force the use of _CRS by specifying "pci=use_crs".
  • The BIOS age is new enough, pci=nocrs is not being used but the kernel has ignored the use of _CRS for some reason.
  • The BIOS age is new enough, pci=crs is being used unnecessarily and the kernel is using _CRS.

Otherwise the test will pass the machine's configuration.


sudo fwts crs - 

..runs the test on your machine and dumps the output to stdout.

sudo fwts crs

..runs the test on your machine and appends the output to the default log results.log.

Explanation of test results

Certain test results may require a little more explanation. This section will try and give some context to specific test failures.

Error ID



BIOS was made before 2008 and is tool old to probably support this feature.


Kernel could not determine the age of the BIOS.


BIOS supports _CRS bridge windows, but has been booted with pci=use_crs which is unnecessary and can be removed.

FirmwareTestSuite/Reference/crs (last edited 2016-01-11 07:24:11 by anthonywong)