[PATCH v3 1/2] xen: Introduce system suspend config option

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

From: Mykyta Poturai <mykyta_poturai@xxxxxxxx>

This option enables the system suspend support. This is the mechanism that
allows the system to be suspended to RAM and later resumed.

The patch introduces three options:
- HAS_SYSTEM_SUSPEND: indicates suspend support is available on the platform.
- SYSTEM_SUSPEND_ALWAYS_ON: used for architectures where suspend must always
  be enabled.
- SYSTEM_SUSPEND: user-facing option to enable/disable suspend if supported.
  Defaults to enabled if SYSTEM_SUSPEND_ALWAYS_ON is set and depends on
  HAS_SYSTEM_SUSPEND.

On x86, both HAS_SYSTEM_SUSPEND and SYSTEM_SUSPEND_ALWAYS_ON are selected by
default, making suspend support always enabled. The options are designed to
be easily extensible to other architectures (e.g., PPC, RISC-V) as future
support is added.

Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
---
Changes introduced in v3:
- select HAS_SYSTEM_SUSPEND from SYSTEM_SUSPEND_ALWAYS_ON
- drop selecting HAS_SYSTEM_SUSPEND from X86
- simplify default setting in SYSTEM_SUSPEND
- hide prompt of SYSTEM_SUSPEND when SYSTEM_SUSPEND_ALWAYS_ON is enabled
- move HAS_SYSTEM_SUSPEND alongside other HAS_* configs

Discussion on adding the SYSTEM_SUSPEND config can be found here:
https://lists.xenproject.org/archives/html/xen-devel/2025-03/msg00169.html
---
 xen/arch/x86/Kconfig |  1 +
 xen/common/Kconfig   | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 7afe879710..752d5141bb 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -33,6 +33,7 @@ config X86
        select HAS_VMAP
        select HAS_VPCI if HVM
        select NEEDS_LIBELF
+       select SYSTEM_SUSPEND_ALWAYS_ON
 
 config ARCH_DEFCONFIG
        string
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index eece1370a3..867710134a 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -122,6 +122,9 @@ config HAS_SCHED_GRANULARITY
 config HAS_STACK_PROTECTOR
        bool
 
+config HAS_SYSTEM_SUSPEND
+       bool
+
 config HAS_UBSAN
        bool
 
@@ -593,4 +596,19 @@ config BUDDY_ALLOCATOR_SIZE
          Amount of memory reserved for the buddy allocator to serve Xen heap,
          working alongside the colored one.
 
+config SYSTEM_SUSPEND_ALWAYS_ON
+       bool
+       select HAS_SYSTEM_SUSPEND
+
+config SYSTEM_SUSPEND
+       bool "System suspend support" if !SYSTEM_SUSPEND_ALWAYS_ON
+       depends on HAS_SYSTEM_SUSPEND
+       default SYSTEM_SUSPEND_ALWAYS_ON
+       help
+         This option enables the system suspend support. This is the
+         mechanism that allows the system to be suspended to RAM and
+         later resumed.
+
+         If unsure, say N.
+
 endmenu
-- 
2.48.1