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>

1 files changed, 62 insertions, 0 deletions

diff --git a/include/linux/soc/apple/tunable.h b/include/linux/soc/apple/tunable.h
new file mode 100644
index 000000000000..531ca814cd02
--- /dev/null
+++ b/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