ACPI: processor idle: Fix up C-state latency if not ordered

Generally, the C-state latency is provided by the _CST method or
FADT, but some OEM platforms using AMD Picasso, Renoir, Van Gogh,
and Cezanne set the C2 latency greater than C3's which causes the
C2 state to be skipped.

That will block the core entering PC6, which prevents S0ix working
properly on Linux systems.

In other operating systems, the latency values are not validated and
this does not cause problems by skipping states.

To avoid this issue on Linux, detect when latencies are not an
arithmetic progression and sort them.

Link: https://gitlab.freedesktop.org/agd5f/linux/-/commit/026d186e4592c1ee9c1cb44295912d0294508725
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1230#note_712174
Suggested-by: Prike Liang <[email protected]>
Suggested-by: Alex Deucher <[email protected]>
Signed-off-by: Mario Limonciello <[email protected]>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

drivers/acpi/processor_idle.c

@@ -16,6 +16,7 @@
 #include <linux/acpi.h>
 #include <linux/dmi.h>
 #include <linux/sched.h>       /* need_resched() */
+#include <linux/sort.h>
 #include <linux/tick.h>
 #include <linux/cpuidle.h>
 #include <linux/cpu.h>
@@ -384,10 +385,37 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr,
 	return;
 }
 
+static int acpi_cst_latency_cmp(const void *a, const void *b)
+{
+	const struct acpi_processor_cx *x = a, *y = b;
+
+	if (!(x->valid && y->valid))
+		return 0;
+	if (x->latency > y->latency)
+		return 1;
+	if (x->latency < y->latency)
+		return -1;
+	return 0;
+}
+static void acpi_cst_latency_swap(void *a, void *b, int n)
+{
+	struct acpi_processor_cx *x = a, *y = b;
+	u32 tmp;
+
+	if (!(x->valid && y->valid))
+		return;
+	tmp = x->latency;
+	x->latency = y->latency;
+	y->latency = tmp;
+}
+
 static int acpi_processor_power_verify(struct acpi_processor *pr)
 {
 	unsigned int i;
 	unsigned int working = 0;
+	unsigned int last_latency = 0;
+	unsigned int last_type = 0;
+	bool buggy_latency = false;
 
 	pr->power.timer_broadcast_on_state = INT_MAX;
 
@@ -411,12 +439,24 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
 		}
 		if (!cx->valid)
 			continue;
+		if (cx->type >= last_type && cx->latency < last_latency)
+			buggy_latency = true;
+		last_latency = cx->latency;
+		last_type = cx->type;
 
 		lapic_timer_check_state(i, pr, cx);
 		tsc_check_state(cx->type);
 		working++;
 	}
 
+	if (buggy_latency) {
+		pr_notice("FW issue: working around C-state latencies out of order\n");
+		sort(&pr->power.states[1], max_cstate,
+		     sizeof(struct acpi_processor_cx),
+		     acpi_cst_latency_cmp,
+		     acpi_cst_latency_swap);
+	}
+
 	lapic_timer_propagate_broadcast(pr);
 
 	return (working);