Users need to set "cpufreq=amd-cppc" in xen cmdline to enable
amd-cppc driver, which selects ACPI Collaborative Performance
and Power Control (CPPC) on supported AMD hardware to provide a
finer grained frequency control mechanism.
`verbose` option can also be included to support verbose print.
When users setting "cpufreq=amd-cppc", a new amd-cppc driver
shall be registered and used. Actual implmentation will be introduced
in the following commits.
Xen is not expected to support both or mixed mode (CPPC & legacy PSS, _PCT,
_PPC) operations, only one cpufreq driver gets registerd, either amd-cppc or
legacy P-states driver, which is reflected and asserted by the incompatible
flags XEN_PROCESSOR_PM_PX and XEN_PROCESSOR_PM_CPPC.
Signed-off-by: Penny Zheng <Penny.Zheng@amd.com>
---
v1 -> v2:
- Obey to alphabetic sorting and also strict it with CONFIG_AMD
- Remove unnecessary empty comment line
- Use __initconst_cf_clobber for pre-filled structure cpufreq_driver
- Make new switch-case code apply to Hygon CPUs too
- Change ENOSYS with EOPNOTSUPP
- Blanks around binary operator
- Change all amd_/-pstate defined values to amd_/-cppc
---
v2 -> v3
- refactor too long lines
- Make sure XEN_PROCESSOR_PM_PX and XEN_PROCESSOR_PM_CPPC incompatible flags
after cpufreq register registrantion
---
docs/misc/xen-command-line.pandoc | 16 +++--
xen/arch/x86/acpi/cpufreq/Makefile | 1 +
xen/arch/x86/acpi/cpufreq/acpi.c | 12 +++-
xen/arch/x86/acpi/cpufreq/amd-cppc.c | 78 +++++++++++++++++++++++
xen/arch/x86/acpi/cpufreq/cpufreq.c | 34 +++++++++-
xen/arch/x86/platform_hypercall.c | 11 +++-
xen/drivers/cpufreq/cpufreq.c | 17 +++++
xen/include/acpi/cpufreq/cpufreq.h | 4 ++
xen/include/acpi/cpufreq/processor_perf.h | 7 +-
xen/include/public/sysctl.h | 1 +
10 files changed, 169 insertions(+), 12 deletions(-)
create mode 100644 xen/arch/x86/acpi/cpufreq/amd-cppc.c
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index a440042471..b3c3ca2377 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -515,7 +515,7 @@ If set, force use of the performance counters for oprofile, rather than detectin
available support.
### cpufreq
-> `= none | {{ <boolean> | xen } { [:[powersave|performance|ondemand|userspace][,[<maxfreq>]][,[<minfreq>]]] } [,verbose]} | dom0-kernel | hwp[:[<hdc>][,verbose]]`
+> `= none | {{ <boolean> | xen } { [:[powersave|performance|ondemand|userspace][,[<maxfreq>]][,[<minfreq>]]] } [,verbose]} | dom0-kernel | hwp[:[<hdc>][,verbose]] | amd-cppc[:[verbose]]`
> Default: `xen`
@@ -526,7 +526,7 @@ choice of `dom0-kernel` is deprecated and not supported by all Dom0 kernels.
* `<maxfreq>` and `<minfreq>` are integers which represent max and min processor frequencies
respectively.
* `verbose` option can be included as a string or also as `verbose=<integer>`
- for `xen`. It is a boolean for `hwp`.
+ for `xen`. It is a boolean for `hwp` and `amd-cppc`.
* `hwp` selects Hardware-Controlled Performance States (HWP) on supported Intel
hardware. HWP is a Skylake+ feature which provides better CPU power
management. The default is disabled. If `hwp` is selected, but hardware
@@ -534,13 +534,17 @@ choice of `dom0-kernel` is deprecated and not supported by all Dom0 kernels.
* `<hdc>` is a boolean to enable Hardware Duty Cycling (HDC). HDC enables the
processor to autonomously force physical package components into idle state.
The default is enabled, but the option only applies when `hwp` is enabled.
+* `amd-cppc` selects ACPI Collaborative Performance and Power Control (CPPC)
+ on supported AMD hardware to provide finer grained frequency control
+ mechanism. The default is disabled.
User could use `;`-separated options to support universal options which they
would like to try on any agnostic platform, *but* under priority order, like
-`cpufreq=hwp;xen,verbose`. This first tries `hwp` and falls back to `xen` if
-unavailable. Note: The `verbose` suboption is handled globally. Setting it
-for either the primary or fallback option applies to both irrespective of where
-it is specified.
+`cpufreq=hwp;amd-cppc;xen,verbose`. This first tries `hwp` on Intel, or
+`amd-cppc` on AMD, and it will fall back to `xen` if unavailable. Note:
+The `verbose` suboption is handled globally. Setting it for either the
+primary or fallback option applies to both irrespective of where it is
+specified.
Note: grub2 requires to escape or quote ';', so `"cpufreq=hwp;xen"` should be
specified within double quotes inside grub.cfg. Refer to the grub2
diff --git a/xen/arch/x86/acpi/cpufreq/Makefile b/xen/arch/x86/acpi/cpufreq/Makefile
index e7dbe434a8..a2ba34bda0 100644
--- a/xen/arch/x86/acpi/cpufreq/Makefile
+++ b/xen/arch/x86/acpi/cpufreq/Makefile
@@ -1,4 +1,5 @@
obj-$(CONFIG_INTEL) += acpi.o
+obj-$(CONFIG_AMD) += amd-cppc.o
obj-y += cpufreq.o
obj-$(CONFIG_INTEL) += hwp.o
obj-$(CONFIG_AMD) += powernow.o
diff --git a/xen/arch/x86/acpi/cpufreq/acpi.c b/xen/arch/x86/acpi/cpufreq/acpi.c
index 0cf94ab2d6..49c1795b25 100644
--- a/xen/arch/x86/acpi/cpufreq/acpi.c
+++ b/xen/arch/x86/acpi/cpufreq/acpi.c
@@ -13,6 +13,7 @@
#include <xen/errno.h>
#include <xen/delay.h>
+#include <xen/domain.h>
#include <xen/param.h>
#include <xen/types.h>
@@ -514,5 +515,14 @@ acpi_cpufreq_driver = {
int __init acpi_cpufreq_register(void)
{
- return cpufreq_register_driver(&acpi_cpufreq_driver);
+ int ret;
+
+ ret = cpufreq_register_driver(&acpi_cpufreq_driver);
+ if ( ret )
+ return ret;
+
+ if ( IS_ENABLED(CONFIG_AMD) )
+ xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;
+
+ return ret;
}
diff --git a/xen/arch/x86/acpi/cpufreq/amd-cppc.c b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
new file mode 100644
index 0000000000..7d482140a2
--- /dev/null
+++ b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * amd-cppc.c - AMD Processor CPPC Frequency Driver
+ *
+ * Copyright (C) 2025 Advanced Micro Devices, Inc. All Rights Reserved.
+ *
+ * Author: Penny Zheng <penny.zheng@amd.com>
+ *
+ * AMD CPPC cpufreq driver introduces a new CPU performance scaling design
+ * for AMD processors using the ACPI Collaborative Performance and Power
+ * Control (CPPC) feature which provides finer grained frequency control range.
+ */
+
+#include <xen/domain.h>
+#include <xen/init.h>
+#include <xen/param.h>
+#include <acpi/cpufreq/cpufreq.h>
+
+static bool __init amd_cppc_handle_option(const char *s, const char *end)
+{
+ int ret;
+
+ ret = parse_boolean("verbose", s, end);
+ if ( ret >= 0 )
+ {
+ cpufreq_verbose = ret;
+ return true;
+ }
+
+ return false;
+}
+
+int __init amd_cppc_cmdline_parse(const char *s, const char *e)
+{
+ do
+ {
+ const char *end = strpbrk(s, ",;");
+
+ if ( !amd_cppc_handle_option(s, end) )
+ {
+ printk(XENLOG_WARNING
+ "cpufreq/amd-cppc: option '%.*s' not recognized\n",
+ (int)((end ?: e) - s), s);
+
+ return -EINVAL;
+ }
+
+ s = end ? end + 1 : NULL;
+ } while ( s && s < e );
+
+ return 0;
+}
+
+static const struct cpufreq_driver __initconst_cf_clobber
+amd_cppc_cpufreq_driver =
+{
+ .name = XEN_AMD_CPPC_DRIVER_NAME,
+};
+
+int __init amd_cppc_register_driver(void)
+{
+ int ret;
+
+ if ( !cpu_has_cppc )
+ {
+ xen_processor_pmbits &= ~XEN_PROCESSOR_PM_CPPC;
+ return -ENODEV;
+ }
+
+ ret = cpufreq_register_driver(&amd_cppc_cpufreq_driver);
+ if ( ret )
+ return ret;
+
+ /* Remove possible fallback option */
+ xen_processor_pmbits &= ~XEN_PROCESSOR_PM_PX;
+
+ return ret;
+}
diff --git a/xen/arch/x86/acpi/cpufreq/cpufreq.c b/xen/arch/x86/acpi/cpufreq/cpufreq.c
index 61e98b67bd..690a285f11 100644
--- a/xen/arch/x86/acpi/cpufreq/cpufreq.c
+++ b/xen/arch/x86/acpi/cpufreq/cpufreq.c
@@ -148,6 +148,10 @@ static int __init cf_check cpufreq_driver_init(void)
case CPUFREQ_none:
ret = 0;
break;
+ default:
+ printk(XENLOG_WARNING
+ "Unsupported cpufreq driver for vendor Intel\n");
+ break;
}
if ( ret != -ENODEV )
@@ -157,7 +161,35 @@ static int __init cf_check cpufreq_driver_init(void)
case X86_VENDOR_AMD:
case X86_VENDOR_HYGON:
- ret = IS_ENABLED(CONFIG_AMD) ? powernow_register_driver() : -ENODEV;
+ if ( !IS_ENABLED(CONFIG_AMD) )
+ {
+ ret = -ENODEV;
+ break;
+ }
+ ret = -ENOENT;
+
+ for ( unsigned int i = 0; i < cpufreq_xen_cnt; i++ )
+ {
+ switch ( cpufreq_xen_opts[i] )
+ {
+ case CPUFREQ_xen:
+ ret = powernow_register_driver();
+ break;
+ case CPUFREQ_amd_cppc:
+ ret = amd_cppc_register_driver();
+ break;
+ case CPUFREQ_none:
+ ret = 0;
+ break;
+ default:
+ printk(XENLOG_WARNING
+ "Unsupported cpufreq driver for vendor AMD\n");
+ break;
+ }
+
+ if ( ret != -ENODEV )
+ break;
+ }
break;
}
}
diff --git a/xen/arch/x86/platform_hypercall.c b/xen/arch/x86/platform_hypercall.c
index 77390a0dbd..5dd1ba2949 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -542,6 +542,7 @@ ret_t do_platform_op(
ret = -ENOSYS;
break;
}
+ ASSERT(!(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC));
ret = set_px_pminfo(op->u.set_pminfo.id, &op->u.set_pminfo.u.perf);
break;
@@ -572,7 +573,8 @@ ret_t do_platform_op(
break;
}
case XEN_PM_PSD:
- if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_PX) )
+ if ( !(xen_processor_pmbits & (XEN_PROCESSOR_PM_PX |
+ XEN_PROCESSOR_PM_CPPC)) )
{
ret = -EOPNOTSUPP;
break;
@@ -584,6 +586,13 @@ ret_t do_platform_op(
break;
case XEN_PM_CPPC:
+ if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
+ {
+ ret = -EOPNOTSUPP;
+ break;
+ }
+ ASSERT(!(xen_processor_pmbits & XEN_PROCESSOR_PM_PX));
+
ret = set_cppc_pminfo(op->u.set_pminfo.id,
&op->u.set_pminfo.u.cppc_data);
break;
diff --git a/xen/drivers/cpufreq/cpufreq.c b/xen/drivers/cpufreq/cpufreq.c
index cfae16c15f..792e4dc02c 100644
--- a/xen/drivers/cpufreq/cpufreq.c
+++ b/xen/drivers/cpufreq/cpufreq.c
@@ -111,6 +111,19 @@ static int __init cpufreq_cmdline_parse_hwp(const char *arg, const char *end)
return ret;
}
+static int __init cpufreq_cmdline_parse_cppc(const char *arg, const char *end)
+{
+ int ret = 0;
+
+ xen_processor_pmbits |= XEN_PROCESSOR_PM_CPPC;
+ cpufreq_controller = FREQCTL_xen;
+ cpufreq_xen_opts[cpufreq_xen_cnt++] = CPUFREQ_amd_cppc;
+ if ( arg[0] && arg[1] )
+ ret = amd_cppc_cmdline_parse(arg + 1, end);
+
+ return ret;
+}
+
static int __init cf_check setup_cpufreq_option(const char *str)
{
const char *arg = strpbrk(str, ",:;");
@@ -159,6 +172,10 @@ static int __init cf_check setup_cpufreq_option(const char *str)
!cmdline_strcmp(str, "hwp") &&
!cpufreq_opts_contain(CPUFREQ_hwp) )
ret = cpufreq_cmdline_parse_hwp(arg, end);
+ else if ( IS_ENABLED(CONFIG_AMD) && choice < 0 &&
+ !cmdline_strcmp(str, "amd-cppc") &&
+ !cpufreq_opts_contain(CPUFREQ_amd_cppc) )
+ ret = cpufreq_cmdline_parse_cppc(arg, end);
else
ret = -EINVAL;
diff --git a/xen/include/acpi/cpufreq/cpufreq.h b/xen/include/acpi/cpufreq/cpufreq.h
index 3f1b05a02e..a6fb10ea27 100644
--- a/xen/include/acpi/cpufreq/cpufreq.h
+++ b/xen/include/acpi/cpufreq/cpufreq.h
@@ -28,6 +28,7 @@ enum cpufreq_xen_opt {
CPUFREQ_none,
CPUFREQ_xen,
CPUFREQ_hwp,
+ CPUFREQ_amd_cppc,
};
extern enum cpufreq_xen_opt cpufreq_xen_opts[2];
extern unsigned int cpufreq_xen_cnt;
@@ -267,4 +268,7 @@ int set_hwp_para(struct cpufreq_policy *policy,
int acpi_cpufreq_register(void);
+int amd_cppc_cmdline_parse(const char *s, const char *e);
+int amd_cppc_register_driver(void);
+
#endif /* __XEN_CPUFREQ_PM_H__ */
diff --git a/xen/include/acpi/cpufreq/processor_perf.h b/xen/include/acpi/cpufreq/processor_perf.h
index 33edf112a0..ee12e0192b 100644
--- a/xen/include/acpi/cpufreq/processor_perf.h
+++ b/xen/include/acpi/cpufreq/processor_perf.h
@@ -6,9 +6,10 @@
#include <xen/acpi.h>
/* ability bits */
-#define XEN_PROCESSOR_PM_CX 1
-#define XEN_PROCESSOR_PM_PX 2
-#define XEN_PROCESSOR_PM_TX 4
+#define XEN_PROCESSOR_PM_CX 1
+#define XEN_PROCESSOR_PM_PX 2
+#define XEN_PROCESSOR_PM_TX 4
+#define XEN_PROCESSOR_PM_CPPC 8
#define XEN_CPPC_INIT 0x40000000U
#define XEN_PX_INIT 0x80000000U
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index b0fec271d3..42997252ef 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -423,6 +423,7 @@ struct xen_set_cppc_para {
uint32_t activity_window;
};
+#define XEN_AMD_CPPC_DRIVER_NAME "amd-cppc"
#define XEN_HWP_DRIVER_NAME "hwp"
/*
--
2.34.1© 2016 - 2025 Red Hat, Inc.