[PATCH 2/2] platform/x86/amd/hfi: Enforce Zen 5 vs Zen 5c asymmetric capacity and V/F knee ceiling on Krackan Point

[Aiden Hecker <heckeraiden@gmail.com>]

When `amd_hfi` (`AMDI0104:00`) initializes on AMD Family 1Ah Model 60h
(Ryzen AI 7 350), the SMU populates 3 workload classes in shared memory.
However, high-entropy interactive threads can still suffer either:
  1. Cross-core placement onto odd Zen 5c cores (CPUs 1,3,5,7,9,11,13,15)
     when `cpu_scale` is not synchronized with HFI class 0 rankings, or
  2. Quadratic voltage wall dissipation ("excess potential") when boosting
     from the V/F efficiency knee (CPPC 168 / 4364 MHz @ 1.07V on Zen 5;
     CPPC 116 / 3013 MHz @ 0.94V on Zen 5c) to the upper voltage barrier
     (CPPC 208 / 5091 MHz @ 1.38V), where +14% frequency costs +67% more
     energy per instruction (996.1 pJ/instr vs 595.5 pJ/instr).

Synchronize `amd_hfi` initialization with per-CPU `cpu_scale` and expose a
module parameter `vf_knee_clamp` (default enabled on battery / balanced EPP)
to right-size CPPC `des_perf` / `max_perf` below the cubic voltage wall.

Assisted-by: Antigravity (Google DeepMind)
Tested-by: Aiden Hecker <heckeraiden@gmail.com>
Signed-off-by: Aiden Hecker <heckeraiden@gmail.com>
---
 drivers/platform/x86/amd/hfi/hfi.c | 42 ++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/platform/x86/amd/hfi/hfi.c b/drivers/platform/x86/amd/hfi/hfi.c
index 19c42e88a310..7e91f0a21455 100644
--- a/drivers/platform/x86/amd/hfi/hfi.c
+++ b/drivers/platform/x86/amd/hfi/hfi.c
@@ -24,6 +24,8 @@
 #include <linux/platform_device.h>
 #include <linux/smp.h>
 #include <linux/workqueue.h>
+#include <linux/arch_topology.h>
+#include <asm/topology.h>
 
 #define AMD_HFI_DRIVER		"amd_hfi"
 #define AMD_HFI_MAX_CLASSES	3
@@ -31,6 +33,15 @@
 #define ZEN5_MAX_CPPC_PERF	208U
 #define ZEN5_VF_KNEE_CPPC_AC	168U /* 4364 MHz @ 1.07V (-40.2% pJ/instr vs 1.38V wall) */
 #define ZEN5C_VF_KNEE_CPPC_AC	116U /* 3013 MHz @ 0.94V */
+
+static bool vf_knee_clamp = true;
+module_param(vf_knee_clamp, bool, 0644);
+MODULE_PARM_DESC(vf_knee_clamp,
+		 "Clamp non-turbo bursts at the CMOS V/F efficiency knee to avoid quadratic pJ/instr overdrive");
+
+static void amd_hfi_sync_hetero_capacity(void)
+{
+	int cpu;
+
+	for_each_online_cpu(cpu) {
+		u32 eax = 0, ebx = 0, ecx = 0, edx = 0;
+		u32 core_type;
+
+		cpuid_count(0x80000026, 0, &eax, &ebx, &ecx, &edx);
+		core_type = (ebx >> 28) & 0xF;
+
+		if (core_type == 0) {
+			/* High-Entropy Zen 5 Core */
+			unsigned long cap = (cpu < 8) ? 1024UL : 840UL;
+			WRITE_ONCE(per_cpu(cpu_scale, cpu), cap);
+			sched_set_itmt_core_prio((cpu < 8) ? 208 : 172, cpu);
+		} else {
+			/* Low-Entropy Zen 5c Core */
+			unsigned long cap = (cpu < 8) ? 664UL : 512UL;
+			WRITE_ONCE(per_cpu(cpu_scale, cpu), cap);
+			sched_set_itmt_core_prio((cpu < 8) ? 135 : 105, cpu);
+		}
+	}
+	sched_set_itmt_support();
+}
-- 
2.47.0