mailbox: Add RP1 mailbox support

The Raspberry Pi RP1 includes 2 M3 cores running firmware. This driver
adds a mailbox communication channel to them via a doorbell and some
shared memory.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/mailbox/Kconfig

@@ -390,4 +390,13 @@ config RISCV_SBI_MPXY_MBOX
 	  or HS-mode hypervisor). Say Y here if you want to have this support.
 	  If unsure say N.
 
+config MBOX_RP1
+	tristate "RP1 Mailbox"
+	depends on MFD_RP1
+	help
+	  An implementation of a mailbox interface to the Raspberry Pi RP1 I/O
+	  interface. Although written as a mailbox driver, the hardware only
+	  provides an array of 32 doorbells.
+	  Say Y here if you want to use the RP1 Mailbox.
+
 endif

drivers/mailbox/Makefile

@@ -82,3 +82,5 @@ obj-$(CONFIG_CIX_MBOX)	+= cix-mailbox.o
 obj-$(CONFIG_BCM74110_MAILBOX)	+= bcm74110-mailbox.o
 
 obj-$(CONFIG_RISCV_SBI_MPXY_MBOX)	+= riscv-sbi-mpxy-mbox.o
+
+obj-$(CONFIG_MBOX_RP1)		+= rp1-mailbox.o

drivers/mailbox/rp1-mailbox.c

@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Copyright (C) 2023 Raspberry Pi Ltd.
+ *
+ * Parts of this driver are based on:
+ *  - bcm2835-mailbox.c
+ *    Copyright (C) 2010,2015 Broadcom
+ *    Copyright (C) 2013-2014 Lubomir Rintel
+ *    Copyright (C) 2013 Craig McGeachie
+ */
+
+#include <linux/compat.h>
+#include <linux/device.h>
+#include <linux/dma-mapping.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/mailbox_controller.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+
+/*
+ * RP1's PROC_EVENTS register can generate interrupts on the M3 cores (when
+ * enabled). The 32-bit register is treated as 32 events, all of which share a
+ * common interrupt. HOST_EVENTS is the same in the reverse direction.
+ */
+#define SYSCFG_PROC_EVENTS		0x00000008
+#define SYSCFG_HOST_EVENTS		0x0000000c
+#define SYSCFG_HOST_EVENT_IRQ_EN	0x00000010
+#define SYSCFG_HOST_EVENT_IRQ		0x00000014
+
+#define HW_SET_BITS			0x00002000
+#define HW_CLR_BITS			0x00003000
+
+#define MAX_CHANS	4 /* 32 is the hardware limit */
+
+struct rp1_mbox {
+	void __iomem *regs;
+	unsigned int irq;
+	struct mbox_controller controller;
+};
+
+static struct rp1_mbox *rp1_chan_mbox(struct mbox_chan *chan)
+{
+	return container_of(chan->mbox, struct rp1_mbox, controller);
+}
+
+static unsigned int rp1_chan_event(struct mbox_chan *chan)
+{
+	return (unsigned int)(uintptr_t)chan->con_priv;
+}
+
+static irqreturn_t rp1_mbox_irq(int irq, void *dev_id)
+{
+	struct rp1_mbox *mbox = dev_id;
+	struct mbox_chan *chan;
+	unsigned int doorbell;
+	unsigned int evs;
+
+	evs = readl(mbox->regs + SYSCFG_HOST_EVENT_IRQ);
+	writel(evs, mbox->regs + SYSCFG_HOST_EVENTS + HW_CLR_BITS);
+
+	while (evs) {
+		doorbell = __ffs(evs);
+		chan = &mbox->controller.chans[doorbell];
+		mbox_chan_received_data(chan, NULL);
+		evs &= ~(1 << doorbell);
+	}
+	return IRQ_HANDLED;
+}
+
+static int rp1_send_data(struct mbox_chan *chan, void *data)
+{
+	struct rp1_mbox *mbox = rp1_chan_mbox(chan);
+	unsigned int event = rp1_chan_event(chan);
+
+	writel(event, mbox->regs + SYSCFG_PROC_EVENTS + HW_SET_BITS);
+
+	return 0;
+}
+
+static int rp1_startup(struct mbox_chan *chan)
+{
+	struct rp1_mbox *mbox = rp1_chan_mbox(chan);
+	unsigned int event = rp1_chan_event(chan);
+
+	writel(event, mbox->regs + SYSCFG_HOST_EVENT_IRQ_EN + HW_SET_BITS);
+
+	return 0;
+}
+
+static void rp1_shutdown(struct mbox_chan *chan)
+{
+	struct rp1_mbox *mbox = rp1_chan_mbox(chan);
+	unsigned int event = rp1_chan_event(chan);
+
+	writel(event, mbox->regs + SYSCFG_HOST_EVENT_IRQ_EN + HW_CLR_BITS);
+}
+
+static bool rp1_last_tx_done(struct mbox_chan *chan)
+{
+	struct rp1_mbox *mbox = rp1_chan_mbox(chan);
+	unsigned int event = rp1_chan_event(chan);
+	unsigned int evs;
+
+	evs = readl(mbox->regs + SYSCFG_HOST_EVENT_IRQ);
+
+	return !(evs & event);
+}
+
+static const struct mbox_chan_ops rp1_mbox_chan_ops = {
+	.send_data	= rp1_send_data,
+	.startup	= rp1_startup,
+	.shutdown	= rp1_shutdown,
+	.last_tx_done	= rp1_last_tx_done
+};
+
+static struct mbox_chan *rp1_mbox_xlate(struct mbox_controller *mbox,
+					const struct of_phandle_args *spec)
+{
+	struct mbox_chan *chan;
+	unsigned int doorbell;
+
+	if (spec->args_count != 1)
+		return ERR_PTR(-EINVAL);
+
+	doorbell = spec->args[0];
+	if (doorbell >= MAX_CHANS)
+		return ERR_PTR(-EINVAL);
+
+	chan = &mbox->chans[doorbell];
+
+	chan->con_priv = (void *)(uintptr_t)(1 << doorbell);
+
+	return chan;
+}
+
+static int rp1_mbox_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct mbox_chan *chans;
+	struct rp1_mbox *mbox;
+	int ret = 0;
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (mbox == NULL)
+		return -ENOMEM;
+
+	ret = devm_request_irq(dev, platform_get_irq(pdev, 0),
+			       rp1_mbox_irq, 0, dev_name(dev), mbox);
+	if (ret) {
+		dev_err(dev, "Failed to register a mailbox IRQ handler: %d\n",
+			ret);
+		return -ENODEV;
+	}
+
+	mbox->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(mbox->regs)) {
+		ret = PTR_ERR(mbox->regs);
+		return ret;
+	}
+
+	chans = devm_kcalloc(dev, MAX_CHANS, sizeof(*chans), GFP_KERNEL);
+	if (!chans)
+		return -ENOMEM;
+
+	mbox->controller.txdone_poll = true;
+	mbox->controller.txpoll_period = 5;
+	mbox->controller.ops = &rp1_mbox_chan_ops;
+	mbox->controller.of_xlate = &rp1_mbox_xlate;
+	mbox->controller.dev = dev;
+	mbox->controller.num_chans = MAX_CHANS;
+	mbox->controller.chans = chans;
+
+	ret = devm_mbox_controller_register(dev, &mbox->controller);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, mbox);
+
+	return 0;
+}
+
+static const struct of_device_id rp1_mbox_of_match[] = {
+	{ .compatible = "raspberrypi,rp1-mbox", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, rp1_mbox_of_match);
+
+static struct platform_driver rp1_mbox_driver = {
+	.driver = {
+		.name = "rp1-mbox",
+		.of_match_table = rp1_mbox_of_match,
+	},
+	.probe = rp1_mbox_probe,
+};
+
+module_platform_driver(rp1_mbox_driver);
+
+MODULE_AUTHOR("Phil Elwell <phil@raspberrypi.com>");
+MODULE_DESCRIPTION("RP1 mailbox IPC driver");
+MODULE_LICENSE("GPL v2");