[V9 1/9] drivers core: Add support for Wifi band RF mitigations

[Evan Quan <evan.quan@amd.com>]

Due to electrical and mechanical constraints in certain platform designs
there may be likely interference of relatively high-powered harmonics of
the (G-)DDR memory clocks with local radio module frequency bands used
by Wifi 6/6e/7.

To mitigate this, AMD has introduced a mechanism that devices can use to
notify active use of particular frequencies so that other devices can make
relative internal adjustments as necessary to avoid this resonance.

In order for a device to support this, the expected flow for device
driver or subsystems:

Drivers/subsystems contributing frequencies:

1) During probe, check `wbrf_supported_producer` to see if WBRF supported
   for the device.
2) If adding frequencies, then call `wbrf_add_exclusion` with the
   start and end ranges of the frequencies.
3) If removing frequencies, then call `wbrf_remove_exclusion` with
   start and end ranges of the frequencies.

Drivers/subsystems responding to frequencies:

1) During probe, check `wbrf_supported_consumer` to see if WBRF is supported
   for the device.
2) Call the `wbrf_register_notifier` to register for notifications of
   frequency changes from other devices.
3) Call the `wbrf_retrieve_exclusions` to retrieve the current exclusions
   range on receiving a notification and response correspondingly.

Meanwhile a kernel parameter `wbrf` with default setting as "auto" is
introduced to specify what the policy is.
  - With `wbrf=on`, the WBRF features will be enabled forcely.
  - With `wbrf=off`, the WBRF features will be disabled forcely.
  - With `wbrf=auto`, it will be up to the system to do proper checks
    to determine the WBRF features should be enabled or not.

Co-developed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Co-developed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Evan Quan <evan.quan@amd.com>
--
v4->v5:
  - promote this to be a more generic solution with input argument taking
    `struct device` and provide better scalability to support non-ACPI
    scenarios(Andrew)
  - update the APIs naming and some other minor fixes(Rafael)
v6->v7:
  - revised the `struct wbrf_ranges_out` to be naturally aligned(Andrew)
  - revised some code comments(Andrew)
v8->v9:
  - update the document to be more readable(Randy)
---
 .../admin-guide/kernel-parameters.txt         |   8 +
 drivers/base/Makefile                         |   1 +
 drivers/base/wbrf.c                           | 280 ++++++++++++++++++
 include/linux/wbrf.h                          |  47 +++
 4 files changed, 336 insertions(+)
 create mode 100644 drivers/base/wbrf.c
 create mode 100644 include/linux/wbrf.h

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a1457995fd41..5566fefeffdf 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7152,3 +7152,11 @@
 				xmon commands.
 			off	xmon is disabled.
 
+	wbrf=		[KNL]
+			Format: { on | auto (default) | off }
+			Controls if WBRF features should be forced on or off.
+			on	Force enable the WBRF features.
+			auto	Up to the system to do proper checks to
+				determine the WBRF features should be enabled
+				or not.
+			off	Force disable the WBRF features.
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 3079bfe53d04..7b3cef898c19 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -26,6 +26,7 @@ obj-$(CONFIG_GENERIC_MSI_IRQ) += platform-msi.o
 obj-$(CONFIG_GENERIC_ARCH_TOPOLOGY) += arch_topology.o
 obj-$(CONFIG_GENERIC_ARCH_NUMA) += arch_numa.o
 obj-$(CONFIG_ACPI) += physical_location.o
+obj-y			+= wbrf.o
 
 obj-y			+= test/
 
diff --git a/drivers/base/wbrf.c b/drivers/base/wbrf.c
new file mode 100644
index 000000000000..678f245c12c6
--- /dev/null
+++ b/drivers/base/wbrf.c
@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Wifi Band Exclusion Interface
+ * Copyright (C) 2023 Advanced Micro Devices
+ *
+ */
+
+#include <linux/wbrf.h>
+
+static BLOCKING_NOTIFIER_HEAD(wbrf_chain_head);
+static DEFINE_MUTEX(wbrf_mutex);
+static enum WBRF_POLICY_MODE {
+	WBRF_POLICY_FORCE_DISABLE,
+	WBRF_POLICY_AUTO,
+	WBRF_POLICY_FORCE_ENABLE,
+} wbrf_policy = WBRF_POLICY_AUTO;
+
+static int __init parse_wbrf_policy_mode(char *p)
+{
+	if (!strncmp(p, "auto", 4))
+		wbrf_policy = WBRF_POLICY_AUTO;
+	else if (!strncmp(p, "on", 2))
+		wbrf_policy = WBRF_POLICY_FORCE_ENABLE;
+	else if (!strncmp(p, "off", 3))
+		wbrf_policy = WBRF_POLICY_FORCE_DISABLE;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+early_param("wbrf", parse_wbrf_policy_mode);
+
+static struct exclusion_range_pool {
+	struct exclusion_range	band_list[MAX_NUM_OF_WBRF_RANGES];
+	u64			ref_counter[MAX_NUM_OF_WBRF_RANGES];
+} wbrf_pool;
+
+static int _wbrf_add_exclusion_ranges(struct wbrf_ranges_in *in)
+{
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(in->band_list); i++) {
+		if (!in->band_list[i].start &&
+		    !in->band_list[i].end)
+			continue;
+
+		for (j = 0; j < ARRAY_SIZE(wbrf_pool.band_list); j++) {
+			if (wbrf_pool.band_list[j].start == in->band_list[i].start &&
+			    wbrf_pool.band_list[j].end == in->band_list[i].end) {
+				wbrf_pool.ref_counter[j]++;
+				break;
+			}
+		}
+		if (j < ARRAY_SIZE(wbrf_pool.band_list))
+			continue;
+
+		for (j = 0; j < ARRAY_SIZE(wbrf_pool.band_list); j++) {
+			if (!wbrf_pool.band_list[j].start &&
+			    !wbrf_pool.band_list[j].end) {
+				wbrf_pool.band_list[j].start = in->band_list[i].start;
+				wbrf_pool.band_list[j].end = in->band_list[i].end;
+				wbrf_pool.ref_counter[j] = 1;
+				break;
+			}
+		}
+		if (j >= ARRAY_SIZE(wbrf_pool.band_list))
+			return -ENOSPC;
+	}
+
+	return 0;
+}
+
+static int _wbrf_remove_exclusion_ranges(struct wbrf_ranges_in *in)
+{
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(in->band_list); i++) {
+		if (!in->band_list[i].start &&
+		    !in->band_list[i].end)
+			continue;
+
+		for (j = 0; j < ARRAY_SIZE(wbrf_pool.band_list); j++) {
+			if (wbrf_pool.band_list[j].start == in->band_list[i].start &&
+			    wbrf_pool.band_list[j].end == in->band_list[i].end) {
+				wbrf_pool.ref_counter[j]--;
+				if (!wbrf_pool.ref_counter[j]) {
+					wbrf_pool.band_list[j].start = 0;
+					wbrf_pool.band_list[j].end = 0;
+				}
+				break;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static int _wbrf_retrieve_exclusion_ranges(struct wbrf_ranges_out *out)
+{
+	int out_idx = 0;
+	int i;
+
+	memset(out, 0, sizeof(*out));
+
+	for (i = 0; i < ARRAY_SIZE(wbrf_pool.band_list); i++) {
+		if (!wbrf_pool.band_list[i].start &&
+		    !wbrf_pool.band_list[i].end)
+			continue;
+
+		out->band_list[out_idx].start = wbrf_pool.band_list[i].start;
+		out->band_list[out_idx++].end = wbrf_pool.band_list[i].end;
+	}
+
+	out->num_of_ranges = out_idx;
+
+	return 0;
+}
+
+/**
+ * wbrf_supported_system - Determine if the system supports WBRF features
+ *
+ * WBRF is used to mitigate devices that cause harmonic interference.
+ * This function will determine if the platform is able to support the
+ * WBRF features.
+ */
+static bool wbrf_supported_system(void)
+{
+	switch (wbrf_policy) {
+	case WBRF_POLICY_FORCE_ENABLE:
+		return true;
+	case WBRF_POLICY_FORCE_DISABLE:
+		return false;
+	case WBRF_POLICY_AUTO:
+		return false;
+	}
+
+	return false;
+}
+
+/**
+ * wbrf_supported_producer - Determine if the device should report frequencies
+ *
+ * @dev: device pointer
+ *
+ * WBRF is used to mitigate devices that cause harmonic interference.
+ * This function will determine if this device should report such frequencies.
+ */
+bool wbrf_supported_producer(struct device *dev)
+{
+	if (!wbrf_supported_system())
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(wbrf_supported_producer);
+
+/**
+ * wbrf_add_exclusion - Add frequency ranges to the exclusion list
+ *
+ * @dev: device pointer
+ * @in: input structure containing the frequency ranges to be added
+ *
+ * Add frequencies into the exclusion list for supported consumers
+ * to react to.
+ */
+int wbrf_add_exclusion(struct device *dev,
+		       struct wbrf_ranges_in *in)
+{
+	int r;
+
+	mutex_lock(&wbrf_mutex);
+
+	r = _wbrf_add_exclusion_ranges(in);
+
+	mutex_unlock(&wbrf_mutex);
+	if (r)
+		return r;
+
+	blocking_notifier_call_chain(&wbrf_chain_head, WBRF_CHANGED, NULL);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(wbrf_add_exclusion);
+
+/**
+ * wbrf_remove_exclusion - Remove frequency ranges from the exclusion list
+ *
+ * @dev: device pointer
+ * @in: input structure containing the frequency ranges to be removed
+ *
+ * Remove frequencies from the exclusion list for supported consumers
+ * to react to.
+ */
+int wbrf_remove_exclusion(struct device *dev,
+			  struct wbrf_ranges_in *in)
+{
+	int r;
+
+	mutex_lock(&wbrf_mutex);
+
+	r = _wbrf_remove_exclusion_ranges(in);
+
+	mutex_unlock(&wbrf_mutex);
+	if (r)
+		return r;
+
+	blocking_notifier_call_chain(&wbrf_chain_head, WBRF_CHANGED, NULL);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(wbrf_remove_exclusion);
+
+/**
+ * wbrf_supported_consumer - Determine if the device should react to frequencies
+ *
+ * @dev: device pointer
+ *
+ * WBRF is used to mitigate devices that cause harmonic interference.
+ * This function will determine if this device should react to reports from
+ * other devices for such frequencies.
+ */
+bool wbrf_supported_consumer(struct device *dev)
+{
+	if (!wbrf_supported_system())
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(wbrf_supported_consumer);
+
+/**
+ * wbrf_register_notifier - Register for notifications of frequency changes
+ *
+ * @nb: driver notifier block
+ *
+ * WBRF is used to mitigate devices that cause harmonic interference.
+ * This function will allow consumers to register for frequency notifications.
+ */
+int wbrf_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&wbrf_chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(wbrf_register_notifier);
+
+/**
+ * wbrf_unregister_notifier - Unregister for notifications of frequency changes
+ *
+ * @nb: driver notifier block
+ *
+ * WBRF is used to mitigate devices that cause harmonic interference.
+ * This function will allow consumers to unregister for frequency notifications.
+ */
+int wbrf_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&wbrf_chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(wbrf_unregister_notifier);
+
+/**
+ * wbrf_retrieve_exclusions - Retrieve the exclusion list
+ *
+ * @dev: device pointer
+ * @out: output structure containing the frequency ranges to be excluded
+ *
+ * Retrieve the current exclusion list
+ */
+int wbrf_retrieve_exclusions(struct device *dev,
+			     struct wbrf_ranges_out *out)
+{
+	int r;
+
+	mutex_lock(&wbrf_mutex);
+
+	r = _wbrf_retrieve_exclusion_ranges(out);
+
+	mutex_unlock(&wbrf_mutex);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(wbrf_retrieve_exclusions);
diff --git a/include/linux/wbrf.h b/include/linux/wbrf.h
new file mode 100644
index 000000000000..476a28fec27a
--- /dev/null
+++ b/include/linux/wbrf.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Wifi Band Exclusion Interface
+ * Copyright (C) 2023 Advanced Micro Devices
+ */
+
+#ifndef _LINUX_WBRF_H
+#define _LINUX_WBRF_H
+
+#include <linux/device.h>
+
+/* Maximum number of wbrf ranges */
+#define MAX_NUM_OF_WBRF_RANGES		11
+
+struct exclusion_range {
+	/* start and end point of the frequency range in Hz */
+	u64		start;
+	u64		end;
+};
+
+struct wbrf_ranges_in {
+	/* valid entry: `start` and `end` filled with non-zero values */
+	struct exclusion_range	band_list[MAX_NUM_OF_WBRF_RANGES];
+};
+
+struct wbrf_ranges_out {
+	u64			num_of_ranges;
+	struct exclusion_range	band_list[MAX_NUM_OF_WBRF_RANGES];
+};
+
+enum wbrf_notifier_actions {
+	WBRF_CHANGED,
+};
+
+bool wbrf_supported_producer(struct device *dev);
+int wbrf_add_exclusion(struct device *adev,
+		       struct wbrf_ranges_in *in);
+int wbrf_remove_exclusion(struct device *dev,
+			  struct wbrf_ranges_in *in);
+int wbrf_retrieve_exclusions(struct device *dev,
+			     struct wbrf_ranges_out *out);
+bool wbrf_supported_consumer(struct device *dev);
+
+int wbrf_register_notifier(struct notifier_block *nb);
+int wbrf_unregister_notifier(struct notifier_block *nb);
+
+#endif /* _LINUX_WBRF_H */
-- 
2.34.1