[tip: x86/urgent] x86/Kconfig: Document CONFIG_PCI_MMCONFIG

[tip-bot2 for Mateusz Jończyk]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     21d8fb8d4e7071b2e60bc48c217ff1b4ce8cb855
Gitweb:        https://git.kernel.org/tip/21d8fb8d4e7071b2e60bc48c217ff1b4ce8cb855
Author:        Mateusz Jończyk <mat.jonczyk@xxxxx>
AuthorDate:    Fri, 21 Mar 2025 21:48:47 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sat, 22 Mar 2025 08:08:20 +01:00

x86/Kconfig: Document CONFIG_PCI_MMCONFIG

This configuration option had no help text, so add it.

CONFIG_EXPERT is enabled on some distribution kernels, so people using a
distribution kernel's configuration as a starting point will see this
option.

[ mingo: Standardized the new Kconfig text a bit. ]

Signed-off-by: Mateusz Jończyk <mat.jonczyk@xxxxx>
Signed-off-by: David Heideberg <david@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250321-x86_x2apic-v3-5-b0cbaa6fa338@xxxxxxx
---
 arch/x86/Kconfig | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 917cd2f..a079ecf 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2902,6 +2902,19 @@ config PCI_MMCONFIG
 	default y
 	depends on PCI && (ACPI || JAILHOUSE_GUEST)
 	depends on X86_64 || (PCI_GOANY || PCI_GOMMCONFIG)
+	help
+	  Add support for accessing the PCI configuration space as a memory
+	  mapped area. It is the recommended method if the system supports
+	  this (it must have PCI Express and ACPI for it to be available).
+
+	  In the unlikely case that enabling this configuration option causes
+	  problems, the mechanism can be switched off with the 'pci=nommconf'
+	  command line parameter.
+
+	  Say N only if you are sure that your platform does not support this
+	  access method or you have problems caused by it.
+
+	  Say Y otherwise.
 
 config PCI_OLPC
 	def_bool y