[PATCH v2 1/3] DT: mailbox: add binding doc for the ARM SMC mailbox

[Andre Przywara]

The ARM SMC mailbox binding describes a firmware interface to trigger
actions in software layers running in the EL2 or EL3 exception levels.
The term "ARM" here relates to the SMC instruction as part of the ARM
instruction set, not as a standard endorsed by ARM Ltd.

Signed-off-by: Andre Przywara <***@arm.com>
---
.../devicetree/bindings/mailbox/arm-smc.txt | 76 ++++++++++++++++++++++
1 file changed, 76 insertions(+)
create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txt

diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.txt b/Documentation/devicetree/bindings/mailbox/arm-smc.txt
new file mode 100644
index 0000000..d9de57b
--- /dev/null
+++ b/Documentation/devicetree/bindings/mailbox/arm-smc.txt
@@ -0,0 +1,76 @@
+ARM SMC Mailbox Interface
+=========================
+
+This mailbox uses the ARM smc (secure monitor call) instruction to
+trigger a mailbox-connected activity in firmware, executing on the very same
+core as the caller. By nature this operation is synchronous and this
+mailbox provides no way for asynchronous messages to be delivered the other
+way round, from firmware to the OS. However the value of r0/w0/x0 the firmware
+returns after the smc call is delivered as a received message to the
+mailbox framework, so a synchronous communication can be established.
+The exact meaning of both the action the mailbox triggers as well as the
+return value is defined by their users and is not subject to this binding.
+
+One use case of this mailbox is the SCP interface, which uses shared memory
+to transfer commands and parameters, and a mailbox to trigger a function
+call. This allows SoCs without a separate management processor (or
+when such a processor is not available or used) to use this standardized
+interface anyway.
+
+This binding describes no hardware, but establishes a firmware interface.
+Upon receiving an SMC using one of the described SMC function identifiers,
+the firmware is expected to trigger some mailbox connected functionality.
+The communication follows the ARM SMC calling convention[1]:
+Firmware expects an SMC function identifier in r0 or w0 to identify a
+particular mailbox. The supported identifiers are listed in the the
+arm,func-ids properties, as described below.
+Apart from those mandatory SMC function identifier there are no further
+arguments handled by the receiving end.
+The firmware can return one value in the first SMC result register, it
+is expected to be an error value, which shall be propagated to the mailbox
+client.
+The C prototype of the function would be:
+ unsigned long smc_mailbox_call(unsigned long mailbox_identifier);
+The SMC function call is expected to be a fast call and could be from
+any of the defined function ranges.
+
+Any core which supports the SMC or HVC instruction can be used, as long as
+a firmware component running in EL3 or EL2 is handling these calls.
+
+Mailbox Device Node:
+====================
+
+This node is expected to be a child of the /firmware node.
+
+Required properties:
+--------------------
+- compatible: Shall be "arm,smc-mbox"
+- #mbox-cells Shall be 1 - the index of the channel needed.
+- arm,func-ids An array of 32-bit values specifying the function
+ IDs used by each mailbox channel. Those function IDs
+ follow the ARM SMC calling convention standard [1].
+ There is one identifier per channel and the number
+ of supported channels is determined by the length
+ of this array.
+- method: A string, either:
+ "hvc": if the driver shall use an HVC call, or
+ "smc": if the driver shall use an SMC call.
+
+Example:
+--------
+
+ smc_mbox: mailbox {
+ #mbox-cells = <1>;
+ compatible = "arm,smc-mbox";
+ arm,func-ids = <0x82000001>, <0x82000002>;
+ };
+
+ scpi {
+ compatible = "arm,scpi";
+ mboxes = <&mailbox 0>;
+ shmem = <&cpu_scp_shmem>;
+ };
+
+
+[1]
+http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0028a/index.html

[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 <***@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 <***@arm.com>");
+MODULE_DESCRIPTION("Generic ARM smc mailbox driver");
+MODULE_LICENSE("GPL v2");

[Andre Przywara]

For 64-bit Allwinner SoCs there exist firmware implementations which
provide SCPI controlled handlers for DVFS, sensors and power domains.
To allow usage of this features, enable the required SMC mailbox when
Allwinner SoCs are supported by the kernel.

Signed-off-by: Andre Przywara <***@arm.com>
---
drivers/mailbox/Kconfig | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index 5664b7f..6d6e8bb 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -174,6 +174,7 @@ config BCM_FLEXRM_MBOX
config ARM_SMC_MBOX
tristate "Generic ARM smc mailbox"
depends on OF && HAVE_ARM_SMCCC
+ default y if ARM64 && ARCH_SUNXI
help
Generic mailbox driver which uses ARM smc calls to call into
firmware for triggering mailboxes.