soc: apple: mailbox: Add ASC/M3 mailbox driver

This new driver is based on the existing apple-mailbox driver, but
replaces the usage of the mailbox subsystem with directly exported
symbols.

As part of this refactor, this adds support for using the hardware FIFOs
(not supported in mailbox) and implicitly fixes a bunch of bugs caused
by bad interactions with the mailbox subsystem. It also adds runtime-PM
support.

The new config symbol is APPLE_MBOX, while the module name remains
identical ("apple-mailbox"). The configs are mutually exclusive in
Kconfig, to avoid conflicts.

Acked-by: Eric Curtin <[e-mail]>
Acked-by: Neal Gompa <[e-mail]>
Acked-by: Alyssa Rosenzweig <[e-mail]>
Signed-off-by: Hector Martin <[e-mail]>

drivers/soc/apple/Kconfig

···
 
 menu "Apple SoC drivers"
 
+config APPLE_MBOX
+	tristate "Apple SoC mailboxes"
+	depends on PM
+	depends on ARCH_APPLE || (64BIT && COMPILE_TEST)
+	depends on !APPLE_MAILBOX
+	default ARCH_APPLE
+	help
+	  Apple SoCs have various co-processors required for certain
+	  peripherals to work (NVMe, display controller, etc.). This
+	  driver adds support for the mailbox controller used to
+	  communicate with those.
+
+	  Say Y here if you have an Apple SoC.
+
 config APPLE_RTKIT
 	tristate "Apple RTKit co-processor IPC protocol"
 	depends on MAILBOX

drivers/soc/apple/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_APPLE_MBOX) += apple-mailbox.o
+apple-mailbox-y = mailbox.o
+
 obj-$(CONFIG_APPLE_RTKIT) += apple-rtkit.o
 apple-rtkit-y = rtkit.o rtkit-crashlog.o
 

drivers/soc/apple/mailbox.c

···
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple mailbox driver
+ *
+ * Copyright The Asahi Linux Contributors
+ *
+ * This driver adds support for two mailbox variants (called ASC and M3 by
+ * Apple) found in Apple SoCs such as the M1. It consists of two FIFOs used to
+ * exchange 64+32 bit messages between the main CPU and a co-processor.
+ * Various coprocessors implement different IPC protocols based on these simple
+ * messages and shared memory buffers.
+ *
+ * Both the main CPU and the co-processor see the same set of registers but
+ * the first FIFO (A2I) is always used to transfer messages from the application
+ * processor (us) to the I/O processor and the second one (I2A) for the
+ * other direction.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/pm_runtime.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include "mailbox.h"
+
+#define APPLE_ASC_MBOX_CONTROL_FULL BIT(16)
+#define APPLE_ASC_MBOX_CONTROL_EMPTY BIT(17)
+
+#define APPLE_ASC_MBOX_A2I_CONTROL 0x110
+#define APPLE_ASC_MBOX_A2I_SEND0 0x800
+#define APPLE_ASC_MBOX_A2I_SEND1 0x808
+#define APPLE_ASC_MBOX_A2I_RECV0 0x810
+#define APPLE_ASC_MBOX_A2I_RECV1 0x818
+
+#define APPLE_ASC_MBOX_I2A_CONTROL 0x114
+#define APPLE_ASC_MBOX_I2A_SEND0 0x820
+#define APPLE_ASC_MBOX_I2A_SEND1 0x828
+#define APPLE_ASC_MBOX_I2A_RECV0 0x830
+#define APPLE_ASC_MBOX_I2A_RECV1 0x838
+
+#define APPLE_M3_MBOX_CONTROL_FULL BIT(16)
+#define APPLE_M3_MBOX_CONTROL_EMPTY BIT(17)
+
+#define APPLE_M3_MBOX_A2I_CONTROL 0x50
+#define APPLE_M3_MBOX_A2I_SEND0 0x60
+#define APPLE_M3_MBOX_A2I_SEND1 0x68
+#define APPLE_M3_MBOX_A2I_RECV0 0x70
+#define APPLE_M3_MBOX_A2I_RECV1 0x78
+
+#define APPLE_M3_MBOX_I2A_CONTROL 0x80
+#define APPLE_M3_MBOX_I2A_SEND0 0x90
+#define APPLE_M3_MBOX_I2A_SEND1 0x98
+#define APPLE_M3_MBOX_I2A_RECV0 0xa0
+#define APPLE_M3_MBOX_I2A_RECV1 0xa8
+
+#define APPLE_M3_MBOX_IRQ_ENABLE 0x48
+#define APPLE_M3_MBOX_IRQ_ACK 0x4c
+#define APPLE_M3_MBOX_IRQ_A2I_EMPTY BIT(0)
+#define APPLE_M3_MBOX_IRQ_A2I_NOT_EMPTY BIT(1)
+#define APPLE_M3_MBOX_IRQ_I2A_EMPTY BIT(2)
+#define APPLE_M3_MBOX_IRQ_I2A_NOT_EMPTY BIT(3)
+
+#define APPLE_MBOX_MSG1_OUTCNT GENMASK(56, 52)
+#define APPLE_MBOX_MSG1_INCNT GENMASK(51, 48)
+#define APPLE_MBOX_MSG1_OUTPTR GENMASK(47, 44)
+#define APPLE_MBOX_MSG1_INPTR GENMASK(43, 40)
+#define APPLE_MBOX_MSG1_MSG GENMASK(31, 0)
+
+#define APPLE_MBOX_TX_TIMEOUT 500
+
+struct apple_mbox_hw {
+	unsigned int control_full;
+	unsigned int control_empty;
+
+	unsigned int a2i_control;
+	unsigned int a2i_send0;
+	unsigned int a2i_send1;
+
+	unsigned int i2a_control;
+	unsigned int i2a_recv0;
+	unsigned int i2a_recv1;
+
+	bool has_irq_controls;
+	unsigned int irq_enable;
+	unsigned int irq_ack;
+	unsigned int irq_bit_recv_not_empty;
+	unsigned int irq_bit_send_empty;
+};
+
+int apple_mbox_send(struct apple_mbox *mbox, const struct apple_mbox_msg msg,
+		    bool atomic)
+{
+	unsigned long flags;
+	int ret;
+	u32 mbox_ctrl;
+	long t;
+
+	spin_lock_irqsave(&mbox->tx_lock, flags);
+	mbox_ctrl = readl_relaxed(mbox->regs + mbox->hw->a2i_control);
+
+	while (mbox_ctrl & mbox->hw->control_full) {
+		if (atomic) {
+			ret = readl_poll_timeout_atomic(
+				mbox->regs + mbox->hw->a2i_control, mbox_ctrl,
+				!(mbox_ctrl & mbox->hw->control_full), 100,
+				APPLE_MBOX_TX_TIMEOUT * 1000);
+
+			if (ret) {
+				spin_unlock_irqrestore(&mbox->tx_lock, flags);
+				return ret;
+			}
+
+			break;
+		}
+		/*
+		 * The interrupt is level triggered and will keep firing as long as the
+		 * FIFO is empty. It will also keep firing if the FIFO was empty
+		 * at any point in the past until it has been acknowledged at the
+		 * mailbox level. By acknowledging it here we can ensure that we will
+		 * only get the interrupt once the FIFO has been cleared again.
+		 * If the FIFO is already empty before the ack it will fire again
+		 * immediately after the ack.
+		 */
+		if (mbox->hw->has_irq_controls) {
+			writel_relaxed(mbox->hw->irq_bit_send_empty,
+				       mbox->regs + mbox->hw->irq_ack);
+		}
+		enable_irq(mbox->irq_send_empty);
+		reinit_completion(&mbox->tx_empty);
+		spin_unlock_irqrestore(&mbox->tx_lock, flags);
+
+		t = wait_for_completion_interruptible_timeout(
+			&mbox->tx_empty,
+			msecs_to_jiffies(APPLE_MBOX_TX_TIMEOUT));
+		if (t < 0)
+			return t;
+		else if (t == 0)
+			return -ETIMEDOUT;
+
+		spin_lock_irqsave(&mbox->tx_lock, flags);
+		mbox_ctrl = readl_relaxed(mbox->regs + mbox->hw->a2i_control);
+	}
+
+	writeq_relaxed(msg.msg0, mbox->regs + mbox->hw->a2i_send0);
+	writeq_relaxed(FIELD_PREP(APPLE_MBOX_MSG1_MSG, msg.msg1),
+		       mbox->regs + mbox->hw->a2i_send1);
+
+	spin_unlock_irqrestore(&mbox->tx_lock, flags);
+
+	return 0;
+}
+EXPORT_SYMBOL(apple_mbox_send);
+
+static irqreturn_t apple_mbox_send_empty_irq(int irq, void *data)
+{
+	struct apple_mbox *mbox = data;
+
+	/*
+	 * We don't need to acknowledge the interrupt at the mailbox level
+	 * here even if supported by the hardware. It will keep firing but that
+	 * doesn't matter since it's disabled at the main interrupt controller.
+	 * apple_mbox_send will acknowledge it before enabling
+	 * it at the main controller again.
+	 */
+	spin_lock(&mbox->tx_lock);
+	disable_irq_nosync(mbox->irq_send_empty);
+	complete(&mbox->tx_empty);
+	spin_unlock(&mbox->tx_lock);
+
+	return IRQ_HANDLED;
+}
+
+static int apple_mbox_poll_locked(struct apple_mbox *mbox)
+{
+	struct apple_mbox_msg msg;
+	int ret = 0;
+
+	u32 mbox_ctrl = readl_relaxed(mbox->regs + mbox->hw->i2a_control);
+
+	while (!(mbox_ctrl & mbox->hw->control_empty)) {
+		msg.msg0 = readq_relaxed(mbox->regs + mbox->hw->i2a_recv0);
+		msg.msg1 = FIELD_GET(
+			APPLE_MBOX_MSG1_MSG,
+			readq_relaxed(mbox->regs + mbox->hw->i2a_recv1));
+
+		mbox->rx(mbox, msg, mbox->cookie);
+		ret++;
+		mbox_ctrl = readl_relaxed(mbox->regs + mbox->hw->i2a_control);
+	}
+
+	/*
+	 * The interrupt will keep firing even if there are no more messages
+	 * unless we also acknowledge it at the mailbox level here.
+	 * There's no race if a message comes in between the check in the while
+	 * loop above and the ack below: If a new messages arrives inbetween
+	 * those two the interrupt will just fire again immediately after the
+	 * ack since it's level triggered.
+	 */
+	if (mbox->hw->has_irq_controls) {
+		writel_relaxed(mbox->hw->irq_bit_recv_not_empty,
+			       mbox->regs + mbox->hw->irq_ack);
+	}
+
+	return ret;
+}
+
+static irqreturn_t apple_mbox_recv_irq(int irq, void *data)
+{
+	struct apple_mbox *mbox = data;
+
+	spin_lock(&mbox->rx_lock);
+	apple_mbox_poll_locked(mbox);
+	spin_unlock(&mbox->rx_lock);
+
+	return IRQ_HANDLED;
+}
+
+int apple_mbox_poll(struct apple_mbox *mbox)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&mbox->rx_lock, flags);
+	ret = apple_mbox_poll_locked(mbox);
+	spin_unlock_irqrestore(&mbox->rx_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL(apple_mbox_poll);
+
+int apple_mbox_start(struct apple_mbox *mbox)
+{
+	int ret;
+
+	if (mbox->active)
+		return 0;
+
+	ret = pm_runtime_resume_and_get(mbox->dev);
+	if (ret)
+		return ret;
+
+	/*
+	 * Only some variants of this mailbox HW provide interrupt control
+	 * at the mailbox level. We therefore need to handle enabling/disabling
+	 * interrupts at the main interrupt controller anyway for hardware that
+	 * doesn't. Just always keep the interrupts we care about enabled at
+	 * the mailbox level so that both hardware revisions behave almost
+	 * the same.
+	 */
+	if (mbox->hw->has_irq_controls) {
+		writel_relaxed(mbox->hw->irq_bit_recv_not_empty |
+				       mbox->hw->irq_bit_send_empty,
+			       mbox->regs + mbox->hw->irq_enable);
+	}
+
+	enable_irq(mbox->irq_recv_not_empty);
+	mbox->active = true;
+	return 0;
+}
+EXPORT_SYMBOL(apple_mbox_start);
+
+void apple_mbox_stop(struct apple_mbox *mbox)
+{
+	if (!mbox->active)
+		return;
+
+	mbox->active = false;
+	disable_irq(mbox->irq_recv_not_empty);
+	pm_runtime_mark_last_busy(mbox->dev);
+	pm_runtime_put_autosuspend(mbox->dev);
+}
+EXPORT_SYMBOL(apple_mbox_stop);
+
+struct apple_mbox *apple_mbox_get(struct device *dev, int index)
+{
+	struct of_phandle_args args;
+	struct platform_device *pdev;
+	struct apple_mbox *mbox;
+	int ret;
+
+	ret = of_parse_phandle_with_args(dev->of_node, "mboxes", "#mbox-cells",
+					 index, &args);
+	if (ret || !args.np)
+		return ERR_PTR(ret);
+
+	pdev = of_find_device_by_node(args.np);
+	of_node_put(args.np);
+
+	if (!pdev)
+		return ERR_PTR(EPROBE_DEFER);
+
+	mbox = platform_get_drvdata(pdev);
+	if (!mbox)
+		return ERR_PTR(EPROBE_DEFER);
+
+	if (!device_link_add(dev, &pdev->dev, DL_FLAG_AUTOREMOVE_CONSUMER))
+		return ERR_PTR(ENODEV);
+
+	return mbox;
+}
+EXPORT_SYMBOL(apple_mbox_get);
+
+struct apple_mbox *apple_mbox_get_byname(struct device *dev, const char *name)
+{
+	int index;
+
+	index = of_property_match_string(dev->of_node, "mbox-names", name);
+	if (index < 0)
+		return ERR_PTR(index);
+
+	return apple_mbox_get(dev, index);
+}
+EXPORT_SYMBOL(apple_mbox_get_byname);
+
+static int apple_mbox_probe(struct platform_device *pdev)
+{
+	int ret;
+	char *irqname;
+	struct apple_mbox *mbox;
+	struct device *dev = &pdev->dev;
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (!mbox)
+		return -ENOMEM;
+
+	mbox->dev = &pdev->dev;
+	mbox->hw = of_device_get_match_data(dev);
+	if (!mbox->hw)
+		return -EINVAL;
+
+	mbox->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(mbox->regs))
+		return PTR_ERR(mbox->regs);
+
+	mbox->irq_recv_not_empty =
+		platform_get_irq_byname(pdev, "recv-not-empty");
+	if (mbox->irq_recv_not_empty < 0)
+		return -ENODEV;
+
+	mbox->irq_send_empty = platform_get_irq_byname(pdev, "send-empty");
+	if (mbox->irq_send_empty < 0)
+		return -ENODEV;
+
+	spin_lock_init(&mbox->rx_lock);
+	spin_lock_init(&mbox->tx_lock);
+	init_completion(&mbox->tx_empty);
+
+	irqname = devm_kasprintf(dev, GFP_KERNEL, "%s-recv", dev_name(dev));
+	if (!irqname)
+		return -ENOMEM;
+
+	ret = devm_request_irq(dev, mbox->irq_recv_not_empty,
+			       apple_mbox_recv_irq,
+			       IRQF_NO_AUTOEN | IRQF_NO_SUSPEND, irqname, mbox);
+	if (ret)
+		return ret;
+
+	irqname = devm_kasprintf(dev, GFP_KERNEL, "%s-send", dev_name(dev));
+	if (!irqname)
+		return -ENOMEM;
+
+	ret = devm_request_irq(dev, mbox->irq_send_empty,
+			       apple_mbox_send_empty_irq,
+			       IRQF_NO_AUTOEN | IRQF_NO_SUSPEND, irqname, mbox);
+	if (ret)
+		return ret;
+
+	ret = devm_pm_runtime_enable(dev);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, mbox);
+	return 0;
+}
+
+static const struct apple_mbox_hw apple_mbox_asc_hw = {
+	.control_full = APPLE_ASC_MBOX_CONTROL_FULL,
+	.control_empty = APPLE_ASC_MBOX_CONTROL_EMPTY,
+
+	.a2i_control = APPLE_ASC_MBOX_A2I_CONTROL,
+	.a2i_send0 = APPLE_ASC_MBOX_A2I_SEND0,
+	.a2i_send1 = APPLE_ASC_MBOX_A2I_SEND1,
+
+	.i2a_control = APPLE_ASC_MBOX_I2A_CONTROL,
+	.i2a_recv0 = APPLE_ASC_MBOX_I2A_RECV0,
+	.i2a_recv1 = APPLE_ASC_MBOX_I2A_RECV1,
+
+	.has_irq_controls = false,
+};
+
+static const struct apple_mbox_hw apple_mbox_m3_hw = {
+	.control_full = APPLE_M3_MBOX_CONTROL_FULL,
+	.control_empty = APPLE_M3_MBOX_CONTROL_EMPTY,
+
+	.a2i_control = APPLE_M3_MBOX_A2I_CONTROL,
+	.a2i_send0 = APPLE_M3_MBOX_A2I_SEND0,
+	.a2i_send1 = APPLE_M3_MBOX_A2I_SEND1,
+
+	.i2a_control = APPLE_M3_MBOX_I2A_CONTROL,
+	.i2a_recv0 = APPLE_M3_MBOX_I2A_RECV0,
+	.i2a_recv1 = APPLE_M3_MBOX_I2A_RECV1,
+
+	.has_irq_controls = true,
+	.irq_enable = APPLE_M3_MBOX_IRQ_ENABLE,
+	.irq_ack = APPLE_M3_MBOX_IRQ_ACK,
+	.irq_bit_recv_not_empty = APPLE_M3_MBOX_IRQ_I2A_NOT_EMPTY,
+	.irq_bit_send_empty = APPLE_M3_MBOX_IRQ_A2I_EMPTY,
+};
+
+static const struct of_device_id apple_mbox_of_match[] = {
+	{ .compatible = "apple,asc-mailbox-v4", .data = &apple_mbox_asc_hw },
+	{ .compatible = "apple,m3-mailbox-v2", .data = &apple_mbox_m3_hw },
+	{}
+};
+MODULE_DEVICE_TABLE(of, apple_mbox_of_match);
+
+static struct platform_driver apple_mbox_driver = {
+	.driver = {
+		.name = "apple-mailbox",
+		.of_match_table = apple_mbox_of_match,
+	},
+	.probe = apple_mbox_probe,
+};
+module_platform_driver(apple_mbox_driver);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_AUTHOR("Sven Peter <[e-mail]>");
+MODULE_DESCRIPTION("Apple Mailbox driver");

drivers/soc/apple/mailbox.h

···
+/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
+/*
+ * Apple mailbox message format
+ *
+ * Copyright The Asahi Linux Contributors
+ */
+
+#ifndef _APPLE_MAILBOX_H_
+#define _APPLE_MAILBOX_H_
+
+#include <linux/device.h>
+#include <linux/types.h>
+
+/* encodes a single 96bit message sent over the single channel */
+struct apple_mbox_msg {
+	u64 msg0;
+	u32 msg1;
+};
+
+struct apple_mbox {
+	struct device *dev;
+	void __iomem *regs;
+	const struct apple_mbox_hw *hw;
+	bool active;
+
+	int irq_recv_not_empty;
+	int irq_send_empty;
+
+	spinlock_t rx_lock;
+	spinlock_t tx_lock;
+
+	struct completion tx_empty;
+
+	/** Receive callback for incoming messages */
+	void (*rx)(struct apple_mbox *mbox, struct apple_mbox_msg msg, void *cookie);
+	void *cookie;
+};
+
+struct apple_mbox *apple_mbox_get(struct device *dev, int index);
+struct apple_mbox *apple_mbox_get_byname(struct device *dev, const char *name);
+
+int apple_mbox_start(struct apple_mbox *mbox);
+void apple_mbox_stop(struct apple_mbox *mbox);
+int apple_mbox_poll(struct apple_mbox *mbox);
+int apple_mbox_send(struct apple_mbox *mbox, struct apple_mbox_msg msg,
+		    bool atomic);
+
+#endif