[PATCH v6 2/6] Documentation/kernel-parameters: Add multi-device config_acs example

Wei Wang
2026-03-12T09:07:04Z

The config_acs parameter allows configuring ACS settings for multiple PCI
devices by separating entries with semicolons. The current documentation
only illustrates applying one configuration pattern to all devices, but
does not show how to specify multiple devices with different ACS settings
in a single parameter. Add an example demonstrating multi-device usage
with distinct ACS configurations.

Some bootloaders interpret ';' as a command separator, which can cause
the parameter to be split as multiple commands. Document that the entire
parameter may need to be quoted to avoid bootloader parsing issues. This
avoids confusing bootloader errors such as ‘can't find command <BDF>’
when passing multiple device entries.

Signed-off-by: Wei Wang <wei.w.wang@hotmail.com>
---
Documentation/admin-guide/kernel-parameters.txt | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 29e0053eb9a5..fe24e5cf4cd0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5320,15 +5320,20 @@ Kernel parameters
'1' – force enabled
'x' – unchanged
For example,
- pci=config_acs=10x@pci:0:0
+ - pci=config_acs=10x@pci:0:0
would configure all devices that support
ACS to enable P2P Request Redirect, disable
Translation Blocking, and leave Source
Validation unchanged from whatever power-up
or firmware set it to.
-
Note: this may remove isolation between devices
and may put more devices in an IOMMU group.
+ - 'pci=config_acs=10x@0000:04:00.0;1x101@0000:84:00.0'
+ configures two devices with different ACS settings.
+ Note: Some bootloaders interpret ';' as a command
+ separator. If so, quote the entire parameter to
+ ensure it is passed to the kernel unchanged.
+
force_floating [S390] Force usage of floating interrupts.
nomio [S390] Do not use MIO instructions.
norid [S390] ignore the RID field and force use of
--
2.51.0