mailbox: add Samsung Exynos driver

The Samsung Exynos mailbox controller, used on Google GS101 SoC, has 16
flag bits for hardware interrupt generation and a shared register for
passing mailbox messages. When the controller is used by the
ACPM interface the shared register is ignored and the mailbox controller
acts as a doorbell. The controller just raises the interrupt to APM
after the ACPM interface has written the message to SRAM.

Add support for the Samsung Exynos mailbox controller.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

drivers/mailbox/Kconfig

@@ -36,6 +36,17 @@ config ARM_MHU_V3
 	  that provides different means of transports: supported extensions
 	  will be discovered and possibly managed at probe-time.
 
+config EXYNOS_MBOX
+	tristate "Exynos Mailbox"
+	depends on ARCH_EXYNOS || COMPILE_TEST
+	help
+	  Say Y here if you want to build the Samsung Exynos Mailbox controller
+	  driver. The controller has 16 flag bits for hardware interrupt
+	  generation and a shared register for passing mailbox messages.
+	  When the controller is used by the ACPM interface the shared register
+	  is ignored and the mailbox controller acts as a doorbell that raises
+	  the interrupt to the ACPM firmware.
+
 config IMX_MBOX
 	tristate "i.MX Mailbox"
 	depends on ARCH_MXC || COMPILE_TEST

drivers/mailbox/Makefile

@@ -11,6 +11,8 @@ obj-$(CONFIG_ARM_MHU_V2)	+= arm_mhuv2.o
 
 obj-$(CONFIG_ARM_MHU_V3)	+= arm_mhuv3.o
 
+obj-$(CONFIG_EXYNOS_MBOX)	+= exynos-mailbox.o
+
 obj-$(CONFIG_IMX_MBOX)	+= imx-mailbox.o
 
 obj-$(CONFIG_ARMADA_37XX_RWTM_MBOX)	+= armada-37xx-rwtm-mailbox.o

drivers/mailbox/exynos-mailbox.c

@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2020 Samsung Electronics Co., Ltd.
+ * Copyright 2020 Google LLC.
+ * Copyright 2024 Linaro Ltd.
+ */
+
+#include <linux/bitops.h>
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/mailbox_controller.h>
+#include <linux/mailbox/exynos-message.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#define EXYNOS_MBOX_MCUCTRL		0x0	/* Mailbox Control Register */
+#define EXYNOS_MBOX_INTCR0		0x24	/* Interrupt Clear Register 0 */
+#define EXYNOS_MBOX_INTMR0		0x28	/* Interrupt Mask Register 0 */
+#define EXYNOS_MBOX_INTSR0		0x2c	/* Interrupt Status Register 0 */
+#define EXYNOS_MBOX_INTMSR0		0x30	/* Interrupt Mask Status Register 0 */
+#define EXYNOS_MBOX_INTGR1		0x40	/* Interrupt Generation Register 1 */
+#define EXYNOS_MBOX_INTMR1		0x48	/* Interrupt Mask Register 1 */
+#define EXYNOS_MBOX_INTSR1		0x4c	/* Interrupt Status Register 1 */
+#define EXYNOS_MBOX_INTMSR1		0x50	/* Interrupt Mask Status Register 1 */
+
+#define EXYNOS_MBOX_INTMR0_MASK		GENMASK(15, 0)
+#define EXYNOS_MBOX_INTGR1_MASK		GENMASK(15, 0)
+
+#define EXYNOS_MBOX_CHAN_COUNT		HWEIGHT32(EXYNOS_MBOX_INTGR1_MASK)
+
+/**
+ * struct exynos_mbox - driver's private data.
+ * @regs:	mailbox registers base address.
+ * @mbox:	pointer to the mailbox controller.
+ * @pclk:	pointer to the mailbox peripheral clock.
+ */
+struct exynos_mbox {
+	void __iomem *regs;
+	struct mbox_controller *mbox;
+	struct clk *pclk;
+};
+
+static int exynos_mbox_send_data(struct mbox_chan *chan, void *data)
+{
+	struct device *dev = chan->mbox->dev;
+	struct exynos_mbox *exynos_mbox = dev_get_drvdata(dev);
+	struct exynos_mbox_msg *msg = data;
+
+	if (msg->chan_id >= exynos_mbox->mbox->num_chans) {
+		dev_err(dev, "Invalid channel ID %d\n", msg->chan_id);
+		return -EINVAL;
+	}
+
+	if (msg->chan_type != EXYNOS_MBOX_CHAN_TYPE_DOORBELL) {
+		dev_err(dev, "Unsupported channel type [%d]\n", msg->chan_type);
+		return -EINVAL;
+	};
+
+	writel(BIT(msg->chan_id), exynos_mbox->regs + EXYNOS_MBOX_INTGR1);
+
+	return 0;
+}
+
+static const struct mbox_chan_ops exynos_mbox_chan_ops = {
+	.send_data = exynos_mbox_send_data,
+};
+
+static struct mbox_chan *exynos_mbox_of_xlate(struct mbox_controller *mbox,
+					      const struct of_phandle_args *sp)
+{
+	int i;
+
+	if (sp->args_count != 0)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Return the first available channel. When we don't pass the
+	 * channel ID from device tree, each channel populated by the driver is
+	 * just a software construct or a virtual channel. We use 'void *data'
+	 * in send_data() to pass the channel identifiers.
+	 */
+	for (i = 0; i < mbox->num_chans; i++)
+		if (mbox->chans[i].cl == NULL)
+			return &mbox->chans[i];
+	return ERR_PTR(-EINVAL);
+}
+
+static const struct of_device_id exynos_mbox_match[] = {
+	{ .compatible = "google,gs101-mbox" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, exynos_mbox_match);
+
+static int exynos_mbox_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct exynos_mbox *exynos_mbox;
+	struct mbox_controller *mbox;
+	struct mbox_chan *chans;
+	int i;
+
+	exynos_mbox = devm_kzalloc(dev, sizeof(*exynos_mbox), GFP_KERNEL);
+	if (!exynos_mbox)
+		return -ENOMEM;
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (!mbox)
+		return -ENOMEM;
+
+	chans = devm_kcalloc(dev, EXYNOS_MBOX_CHAN_COUNT, sizeof(*chans),
+			     GFP_KERNEL);
+	if (!chans)
+		return -ENOMEM;
+
+	exynos_mbox->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(exynos_mbox->regs))
+		return PTR_ERR(exynos_mbox->regs);
+
+	exynos_mbox->pclk = devm_clk_get_enabled(dev, "pclk");
+	if (IS_ERR(exynos_mbox->pclk))
+		return dev_err_probe(dev, PTR_ERR(exynos_mbox->pclk),
+				     "Failed to enable clock.\n");
+
+	mbox->num_chans = EXYNOS_MBOX_CHAN_COUNT;
+	mbox->chans = chans;
+	mbox->dev = dev;
+	mbox->ops = &exynos_mbox_chan_ops;
+	mbox->of_xlate = exynos_mbox_of_xlate;
+
+	for (i = 0; i < EXYNOS_MBOX_CHAN_COUNT; i++)
+		chans[i].mbox = mbox;
+
+	exynos_mbox->mbox = mbox;
+
+	platform_set_drvdata(pdev, exynos_mbox);
+
+	/* Mask out all interrupts. We support just polling channels for now. */
+	writel(EXYNOS_MBOX_INTMR0_MASK, exynos_mbox->regs + EXYNOS_MBOX_INTMR0);
+
+	return devm_mbox_controller_register(dev, mbox);
+}
+
+static struct platform_driver exynos_mbox_driver = {
+	.probe	= exynos_mbox_probe,
+	.driver	= {
+		.name = "exynos-acpm-mbox",
+		.of_match_table	= exynos_mbox_match,
+	},
+};
+module_platform_driver(exynos_mbox_driver);
+
+MODULE_AUTHOR("Tudor Ambarus <tudor.ambarus@linaro.org>");
+MODULE_DESCRIPTION("Samsung Exynos mailbox driver");
+MODULE_LICENSE("GPL");

include/linux/mailbox/exynos-message.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Exynos mailbox message.
+ *
+ * Copyright 2024 Linaro Ltd.
+ */
+
+#ifndef _LINUX_EXYNOS_MESSAGE_H_
+#define _LINUX_EXYNOS_MESSAGE_H_
+
+#define EXYNOS_MBOX_CHAN_TYPE_DOORBELL		0
+#define EXYNOS_MBOX_CHAN_TYPE_DATA		1
+
+struct exynos_mbox_msg {
+	unsigned int chan_id;
+	unsigned int chan_type;
+};
+
+#endif /* _LINUX_EXYNOS_MESSAGE_H_ */