[PATCH v2 2/3] mailbox: introduce ARM SMC based mailbox

[Andre Przywara]

This mailbox driver implements a mailbox which signals transmitted data
via an ARM smc (secure monitor call) instruction. The mailbox receiver
is implemented in firmware and can synchronously return data when it
returns execution to the non-secure world again.
An asynchronous receive path is not implemented.
This allows the usage of a mailbox to trigger firmware actions on SoCs
which either don't have a separate management processor or on which such
a core is not available. A user of this mailbox could be the SCP
interface.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
 drivers/mailbox/Kconfig           |   8 ++
 drivers/mailbox/Makefile          |   2 +
 drivers/mailbox/arm-smc-mailbox.c | 155 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 165 insertions(+)
 create mode 100644 drivers/mailbox/arm-smc-mailbox.c

diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index c5731e5..5664b7f 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -170,4 +170,12 @@ config BCM_FLEXRM_MBOX
 	  Mailbox implementation of the Broadcom FlexRM ring manager,
 	  which provides access to various offload engines on Broadcom
 	  SoCs. Say Y here if you want to use the Broadcom FlexRM.
+
+config ARM_SMC_MBOX
+	tristate "Generic ARM smc mailbox"
+	depends on OF && HAVE_ARM_SMCCC
+	help
+	  Generic mailbox driver which uses ARM smc calls to call into
+	  firmware for triggering mailboxes.
+
 endif
diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
index d54e412..8ec6869 100644
--- a/drivers/mailbox/Makefile
+++ b/drivers/mailbox/Makefile
@@ -35,3 +35,5 @@ obj-$(CONFIG_BCM_FLEXRM_MBOX)	+= bcm-flexrm-mailbox.o
 obj-$(CONFIG_QCOM_APCS_IPC)	+= qcom-apcs-ipc-mailbox.o
 
 obj-$(CONFIG_TEGRA_HSP_MBOX)	+= tegra-hsp.o
+
+obj-$(CONFIG_ARM_SMC_MBOX)	+= arm-smc-mailbox.o
diff --git a/drivers/mailbox/arm-smc-mailbox.c b/drivers/mailbox/arm-smc-mailbox.c
new file mode 100644
index 0000000..d7b61a7
--- /dev/null
+++ b/drivers/mailbox/arm-smc-mailbox.c
@@ -0,0 +1,155 @@
+/*
+ *  Copyright (C) 2016,2017 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This device provides a mechanism for emulating a mailbox by using
+ * smc calls, allowing a "mailbox" consumer to sit in firmware running
+ * on the same core.
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/mailbox_controller.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/arm-smccc.h>
+
+#define ARM_SMC_MBOX_USE_HVC	BIT(0)
+
+struct arm_smc_chan_data {
+	u32 function_id;
+	u32 flags;
+};
+
+static int arm_smc_send_data(struct mbox_chan *link, void *data)
+{
+	struct arm_smc_chan_data *chan_data = link->con_priv;
+	u32 function_id = chan_data->function_id;
+	struct arm_smccc_res res;
+	u32 msg = *(u32 *)data;
+
+	if (chan_data->flags & ARM_SMC_MBOX_USE_HVC)
+		arm_smccc_hvc(function_id, msg, 0, 0, 0, 0, 0, 0, &res);
+	else
+		arm_smccc_smc(function_id, msg, 0, 0, 0, 0, 0, 0, &res);
+
+	mbox_chan_received_data(link, (void *)res.a0);
+
+	return 0;
+}
+
+/* This mailbox is synchronous, so we are always done. */
+static bool arm_smc_last_tx_done(struct mbox_chan *link)
+{
+	return true;
+}
+
+static const struct mbox_chan_ops arm_smc_mbox_chan_ops = {
+	.send_data	= arm_smc_send_data,
+	.last_tx_done	= arm_smc_last_tx_done
+};
+
+static int arm_smc_mbox_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct mbox_controller *mbox;
+	struct arm_smc_chan_data *chan_data;
+	const char *method;
+	bool use_hvc = false;
+	int ret, i;
+
+	ret = of_property_count_elems_of_size(dev->of_node, "arm,func-ids",
+					      sizeof(u32));
+	if (ret < 0)
+		return ret;
+
+	if (!of_property_read_string(dev->of_node, "method", &method)) {
+		if (!strcmp("hvc", method)) {
+			use_hvc = true;
+		} else if (!strcmp("smc", method)) {
+			use_hvc = false;
+		} else {
+			dev_warn(dev, "invalid \"method\" property: %s\n",
+				 method);
+
+			return -EINVAL;
+		}
+	}
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (!mbox)
+		return -ENOMEM;
+
+	mbox->num_chans = ret;
+	mbox->chans = devm_kcalloc(dev, mbox->num_chans, sizeof(*mbox->chans),
+				   GFP_KERNEL);
+	if (!mbox->chans)
+		return -ENOMEM;
+
+	chan_data = devm_kcalloc(dev, mbox->num_chans, sizeof(*chan_data),
+				 GFP_KERNEL);
+	if (!chan_data)
+		return -ENOMEM;
+
+	for (i = 0; i < mbox->num_chans; i++) {
+		u32 function_id;
+
+		ret = of_property_read_u32_index(dev->of_node,
+						 "arm,func-ids", i,
+						 &function_id);
+		if (ret)
+			return ret;
+
+		chan_data[i].function_id = function_id;
+		if (use_hvc)
+			chan_data[i].flags |= ARM_SMC_MBOX_USE_HVC;
+		mbox->chans[i].con_priv = &chan_data[i];
+	}
+
+	mbox->txdone_poll = true;
+	mbox->txdone_irq = false;
+	mbox->txpoll_period = 1;
+	mbox->ops = &arm_smc_mbox_chan_ops;
+	mbox->dev = dev;
+
+	ret = mbox_controller_register(mbox);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, mbox);
+	dev_info(dev, "ARM SMC mailbox enabled with %d chan%s.\n",
+		 mbox->num_chans, mbox->num_chans == 1 ? "" : "s");
+
+	return ret;
+}
+
+static int arm_smc_mbox_remove(struct platform_device *pdev)
+{
+	struct mbox_controller *mbox = platform_get_drvdata(pdev);
+
+	mbox_controller_unregister(mbox);
+	return 0;
+}
+
+static const struct of_device_id arm_smc_mbox_of_match[] = {
+	{ .compatible = "arm,smc-mbox", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, arm_smc_mbox_of_match);
+
+static struct platform_driver arm_smc_mbox_driver = {
+	.driver = {
+		.name = "arm-smc-mbox",
+		.of_match_table = arm_smc_mbox_of_match,
+	},
+	.probe		= arm_smc_mbox_probe,
+	.remove		= arm_smc_mbox_remove,
+};
+module_platform_driver(arm_smc_mbox_driver);
+
+MODULE_AUTHOR("Andre Przywara <andre.przywara at arm.com>");
+MODULE_DESCRIPTION("Generic ARM smc mailbox driver");
+MODULE_LICENSE("GPL v2");
-- 
2.8.2