soc: apple: Add hardware tunable support

Various hardware, like the Type-C PHY or the Thunderbolt/USB4 NHI,
present on Apple SoCs need machine-specific tunables passed from our
bootloader m1n1 to the device tree. Add generic helpers so that we
don't have to duplicate this across multiple drivers.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Janne Grunau <j@jannau.net>
Signed-off-by: Sven Peter <sven@kernel.org>
Link: https://patch.msgid.link/20251214-b4-atcphy-v3-1-ba82b20e9459@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soc/apple/Kconfig

@@ -38,6 +38,10 @@ config APPLE_SART
 
 	  Say 'y' here if you have an Apple SoC.
 
+config APPLE_TUNABLE
+	tristate
+	depends on ARCH_APPLE || COMPILE_TEST
+
 endmenu
 
 endif

drivers/soc/apple/Makefile

@@ -8,3 +8,6 @@ apple-rtkit-y = rtkit.o rtkit-crashlog.o
 
 obj-$(CONFIG_APPLE_SART) += apple-sart.o
 apple-sart-y = sart.o
+
+obj-$(CONFIG_APPLE_TUNABLE) += apple-tunable.o
+apple-tunable-y = tunable.o

drivers/soc/apple/tunable.c

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple Silicon hardware tunable support
+ *
+ * Each tunable is a list with each entry containing a offset into the MMIO
+ * region, a mask of bits to be cleared and a set of bits to be set. These
+ * tunables are passed along by the previous boot stages and vary from device
+ * to device such that they cannot be hardcoded in the individual drivers.
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/overflow.h>
+#include <linux/soc/apple/tunable.h>
+
+struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
+					       struct device_node *np,
+					       const char *name,
+					       struct resource *res)
+{
+	struct apple_tunable *tunable;
+	struct property *prop;
+	const __be32 *p;
+	size_t sz;
+	int i;
+
+	if (resource_size(res) < 4)
+		return ERR_PTR(-EINVAL);
+
+	prop = of_find_property(np, name, NULL);
+	if (!prop)
+		return ERR_PTR(-ENOENT);
+
+	if (prop->length % (3 * sizeof(u32)))
+		return ERR_PTR(-EINVAL);
+	sz = prop->length / (3 * sizeof(u32));
+
+	tunable = devm_kzalloc(dev, struct_size(tunable, values, sz), GFP_KERNEL);
+	if (!tunable)
+		return ERR_PTR(-ENOMEM);
+	tunable->sz = sz;
+
+	for (i = 0, p = NULL; i < tunable->sz; ++i) {
+		p = of_prop_next_u32(prop, p, &tunable->values[i].offset);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].mask);
+		p = of_prop_next_u32(prop, p, &tunable->values[i].value);
+
+		/* Sanity checks to catch bugs in our bootloader */
+		if (tunable->values[i].offset % 4)
+			return ERR_PTR(-EINVAL);
+		if (tunable->values[i].offset > (resource_size(res) - 4))
+			return ERR_PTR(-EINVAL);
+	}
+
+	return tunable;
+}
+EXPORT_SYMBOL(devm_apple_tunable_parse);
+
+void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable)
+{
+	size_t i;
+
+	for (i = 0; i < tunable->sz; ++i) {
+		u32 val, old_val;
+
+		old_val = readl(regs + tunable->values[i].offset);
+		val = old_val & ~tunable->values[i].mask;
+		val |= tunable->values[i].value;
+		if (val != old_val)
+			writel(val, regs + tunable->values[i].offset);
+	}
+}
+EXPORT_SYMBOL(apple_tunable_apply);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_AUTHOR("Sven Peter <sven@kernel.org>");
+MODULE_DESCRIPTION("Apple Silicon hardware tunable support");

include/linux/soc/apple/tunable.h

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
+/*
+ * Apple Silicon hardware tunable support
+ *
+ * Each tunable is a list with each entry containing a offset into the MMIO
+ * region, a mask of bits to be cleared and a set of bits to be set. These
+ * tunables are passed along by the previous boot stages and vary from device
+ * to device such that they cannot be hardcoded in the individual drivers.
+ *
+ * Copyright (C) The Asahi Linux Contributors
+ */
+
+#ifndef _LINUX_SOC_APPLE_TUNABLE_H_
+#define _LINUX_SOC_APPLE_TUNABLE_H_
+
+#include <linux/device.h>
+#include <linux/types.h>
+
+/**
+ * Struct to store an Apple Silicon hardware tunable.
+ *
+ * Each tunable is a list with each entry containing a offset into the MMIO
+ * region, a mask of bits to be cleared and a set of bits to be set. These
+ * tunables are passed along by the previous boot stages and vary from device
+ * to device such that they cannot be hardcoded in the individual drivers.
+ *
+ * @param sz Number of [offset, mask, value] tuples stored in values.
+ * @param values [offset, mask, value] array.
+ */
+struct apple_tunable {
+	size_t sz;
+	struct {
+		u32 offset;
+		u32 mask;
+		u32 value;
+	} values[] __counted_by(sz);
+};
+
+/**
+ * Parse an array of hardware tunables from the device tree.
+ *
+ * @dev: Device node used for devm_kzalloc internally.
+ * @np: Device node which contains the tunable array.
+ * @name: Name of the device tree property which contains the tunables.
+ * @res: Resource to which the tunables will be applied, used for bound checking
+ *
+ * @return: devres allocated struct on success or PTR_ERR on failure.
+ */
+struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
+					       struct device_node *np,
+					       const char *name,
+					       struct resource *res);
+
+/**
+ * Apply a previously loaded hardware tunable.
+ *
+ * @param regs: MMIO to which the tunable will be applied.
+ * @param tunable: Pointer to the tunable.
+ */
+void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable);
+
+#endif