mailbox: add driver for Apple ASC mailboxes

Apple ASC mailboxes are used on their M1 SoC to communicate with various
co-processors. They are backed by a single hardware FIFO which can buffer
up to eight 96bit messages.

drivers/mailbox/Kconfig

@@ -8,6 +8,15 @@ menuconfig MAILBOX
 
 if MAILBOX
 
+config APPLE_MBOX
+	tristate "Apple ASC mailbox driver"
+	depends on ARCH_APPLE || COMPILE_TEST
+	default ARCH_APPLE
+	help
+	  Say Y here if you want to build the Apple ASC mailbox driver.
+	  Apple SoCs have various co-processors (NVME, display controller, etc.)
+	  which communicate with the main processor using these mailboxes.
+
 config ARM_MHU
 	tristate "ARM MHU Mailbox"
 	depends on ARM_AMBA

drivers/mailbox/Makefile

@@ -58,3 +58,5 @@ obj-$(CONFIG_SUN6I_MSGBOX)	+= sun6i-msgbox.o
 obj-$(CONFIG_SPRD_MBOX)		+= sprd-mailbox.o
 
 obj-$(CONFIG_QCOM_IPCC)		+= qcom-ipcc.o
+
+obj-$(CONFIG_APPLE_MBOX)	+= apple-asc-mailbox.o

drivers/mailbox/apple-asc-mailbox.c

@@ -0,0 +1,264 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Apple ASC mailbox driver
+ *
+ * Copyright (C) 2021 The Asahi Linux Contributors
+ *
+ * This mailbox hardware consists of two FIFOs used to exchange 64+32 bit
+ * messages between the main CPU and a co-processor. Multiple instances
+ * of this mailbox can be found on Apple SoCs.
+ * Various clients 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/apple-mailbox.h>
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/gfp.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/lockdep.h>
+#include <linux/mailbox_controller.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#define APPLE_ASC_MBOX_A2I_CONTROL 0x110
+#define APPLE_ASC_MBOX_I2A_CONTROL 0x114
+#define APPLE_ASC_MBOX_CONTROL_FULL BIT(16)
+#define APPLE_ASC_MBOX_CONTROL_EMPTY BIT(17)
+
+#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_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_ASC_MBOX_MSG1_OUTCNT GENMASK(56, 52)
+#define APPLE_ASC_MBOX_MSG1_INCNT GENMASK(51, 48)
+#define APPLE_ASC_MBOX_MSG1_OUTPTR GENMASK(47, 44)
+#define APPLE_ASC_MBOX_MSG1_INPTR GENMASK(43, 40)
+#define APPLE_ASC_MBOX_MSG1_MSG GENMASK(31, 0)
+
+struct apple_mbox {
+	void __iomem *regs;
+	int irq_recv_not_empty;
+	int irq_send_empty;
+
+	struct clk_bulk_data *clks;
+	int num_clks;
+
+	struct mbox_chan chan;
+
+	struct device *dev;
+	struct mbox_controller controller;
+};
+
+static bool apple_mbox_hw_can_send(struct apple_mbox *apple_mbox)
+{
+	u32 mbox_ctrl =
+		readl_relaxed(apple_mbox->regs + APPLE_ASC_MBOX_A2I_CONTROL);
+
+	return !(mbox_ctrl & APPLE_ASC_MBOX_CONTROL_FULL);
+}
+
+static void apple_mbox_hw_send(struct apple_mbox *apple_mbox,
+			       struct apple_mbox_msg *msg)
+{
+	WARN_ON(!apple_mbox_hw_can_send(apple_mbox));
+	writeq_relaxed(msg->msg0, apple_mbox->regs + APPLE_ASC_MBOX_A2I_SEND0);
+
+	/*
+	 * we need a DMA barrier here since this message might be related to
+	 * data stored in a shared memory buffer.
+	 */
+	writeq(FIELD_PREP(APPLE_ASC_MBOX_MSG1_MSG, msg->msg1),
+	       apple_mbox->regs + APPLE_ASC_MBOX_A2I_SEND1);
+}
+
+static bool apple_mbox_hw_can_recv(struct apple_mbox *apple_mbox)
+{
+	u32 mbox_ctrl =
+		readl_relaxed(apple_mbox->regs + APPLE_ASC_MBOX_I2A_CONTROL);
+
+	return !(mbox_ctrl & APPLE_ASC_MBOX_CONTROL_EMPTY);
+}
+
+static void apple_mbox_hw_recv(struct apple_mbox *apple_mbox,
+			       struct apple_mbox_msg *msg)
+{
+	WARN_ON(!apple_mbox_hw_can_recv(apple_mbox));
+	msg->msg0 = readq_relaxed(apple_mbox->regs + APPLE_ASC_MBOX_I2A_RECV0);
+
+	/*
+	 * we need a DMA barrier here since this message might be related to
+	 * data stored in a shared memory buffer.
+	 */
+	msg->msg1 =
+		FIELD_GET(APPLE_ASC_MBOX_MSG1_MSG,
+			  readq(apple_mbox->regs + APPLE_ASC_MBOX_I2A_RECV1));
+}
+
+static int apple_mbox_chan_send_data(struct mbox_chan *chan, void *data)
+{
+	struct apple_mbox *apple_mbox = chan->con_priv;
+	struct apple_mbox_msg *msg = data;
+
+	if (!apple_mbox_hw_can_send(apple_mbox))
+		return -EBUSY;
+	apple_mbox_hw_send(apple_mbox, msg);
+	return 0;
+}
+
+static irqreturn_t apple_mbox_send_empty_irq(int irq, void *data)
+{
+	struct apple_mbox *apple_mbox = data;
+
+	disable_irq_nosync(apple_mbox->irq_send_empty);
+	mbox_chan_txready(&apple_mbox->chan);
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t apple_mbox_recv_irq(int irq, void *data)
+{
+	struct apple_mbox *apple_mbox = data;
+	struct apple_mbox_msg msg;
+
+	while (apple_mbox_hw_can_recv(apple_mbox)) {
+		apple_mbox_hw_recv(apple_mbox, &msg);
+		mbox_chan_received_data(&apple_mbox->chan, (void *)&msg);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static struct mbox_chan *apple_mbox_of_xlate(struct mbox_controller *mbox,
+					     const struct of_phandle_args *spec)
+{
+	struct apple_mbox *apple_mbox = dev_get_drvdata(mbox->dev);
+
+	if (spec->args_count != 0)
+		return ERR_PTR(-EINVAL);
+	if (apple_mbox->chan.con_priv)
+		return ERR_PTR(-EBUSY);
+
+	apple_mbox->chan.con_priv = apple_mbox;
+	return &apple_mbox->chan;
+}
+
+static int apple_mbox_chan_startup(struct mbox_chan *chan)
+{
+	struct apple_mbox *apple_mbox = chan->con_priv;
+	enable_irq(apple_mbox->irq_recv_not_empty);
+	return 0;
+}
+
+static void apple_mbox_chan_shutdown(struct mbox_chan *chan)
+{
+	struct apple_mbox *apple_mbox = chan->con_priv;
+	disable_irq(apple_mbox->irq_recv_not_empty);
+}
+
+static void apple_mbox_chan_request_irq(struct mbox_chan *chan)
+{
+	struct apple_mbox *apple_mbox = chan->con_priv;
+	enable_irq(apple_mbox->irq_send_empty);
+}
+
+static const struct mbox_chan_ops apple_mbox_ops = {
+	.send_data = apple_mbox_chan_send_data,
+	.request_irq = apple_mbox_chan_request_irq,
+	.startup = apple_mbox_chan_startup,
+	.shutdown = apple_mbox_chan_shutdown,
+};
+
+static int apple_mbox_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct apple_mbox *mbox;
+	struct device *dev = &pdev->dev;
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (!mbox)
+		return -ENOMEM;
+	platform_set_drvdata(pdev, mbox);
+
+	mbox->dev = dev;
+	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;
+
+	ret = devm_clk_bulk_get_all(dev, &mbox->clks);
+	if (ret)
+		return ret;
+	mbox->num_clks = ret;
+
+	ret = clk_bulk_prepare_enable(mbox->num_clks, mbox->clks);
+	if (ret)
+		return ret;
+
+	mbox->controller.dev = mbox->dev;
+	mbox->controller.num_chans = 1;
+	mbox->controller.chans = &mbox->chan;
+	mbox->controller.ops = &apple_mbox_ops;
+	mbox->controller.of_xlate = &apple_mbox_of_xlate;
+	mbox->controller.txdone_fifo = true;
+
+	ret = devm_request_irq(dev, mbox->irq_recv_not_empty,
+			       apple_mbox_recv_irq, IRQF_NO_AUTOEN,
+			       dev_name(dev), mbox);
+	if (ret)
+		goto err_clk_disable;
+	ret = devm_request_irq(dev, mbox->irq_send_empty,
+			       apple_mbox_send_empty_irq, IRQF_NO_AUTOEN,
+			       dev_name(dev), mbox);
+	if (ret)
+		goto err_clk_disable;
+
+	ret = devm_mbox_controller_register(dev, &mbox->controller);
+	if (ret)
+		goto err_clk_disable;
+	return ret;
+
+err_clk_disable:
+	clk_bulk_disable_unprepare(mbox->num_clks, mbox->clks);
+	return ret;
+}
+
+static const struct of_device_id apple_mbox_of_match[] = {
+	{ .compatible = "apple,t8103-asc-mailbox", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, apple_mbox_of_match);
+
+static struct platform_driver apple_mbox_driver = {
+	.driver = {
+		.name = "apple-asc-mailbox",
+		.of_match_table = apple_mbox_of_match,
+	},
+	.probe = apple_mbox_probe,
+};
+module_platform_driver(apple_mbox_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Sven Peter <sven@svenpeter.dev>");
+MODULE_DESCRIPTION("Apple ASC Mailbox driver");

include/linux/apple-mailbox.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Apple mailbox message format
+ *
+ * Copyright (C) 2021 The Asahi Linux Contributors
+ */
+
+#ifndef _LINUX_APPLE_MAILBOX_H_
+#define _LINUX_APPLE_MAILBOX_H_
+
+#include <linux/types.h>
+
+struct apple_mbox_msg {
+	u64 msg0;
+	u32 msg1;
+};
+
+#endif