Date:   Thu, 5 Nov 2020 22:21:16 +0100
From:   Peter Hilber <peter.hilber@...nsynergy.com>
To:     <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>,
        <virtio-dev@...ts.oasis-open.org>
CC:     Igor Skalkin <igor.skalkin@...nsynergy.com>,
        Peter Hilber <peter.hilber@...nsynergy.com>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-kernel@...r.kernel.org>, <sudeep.holla@....com>,
        <souvik.chakravarty@....com>, <alex.bennee@...aro.org>,
        <jean-philippe@...aro.org>, <mikhail.golubev@...nsynergy.com>,
        <anton.yakovlev@...nsynergy.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Subject: [RFC PATCH v2 10/10] firmware: arm_scmi: Add virtio transport

From: Igor Skalkin <igor.skalkin@...nsynergy.com>

This transport enables accessing an SCMI platform as a virtio device.

Implement an SCMI virtio driver according to the virtio SCMI device spec
patch v5 [1]. Virtio device id 32 has been reserved for the SCMI device
[2].

The virtio transport has one tx channel (virtio cmdq, A2P channel) and
at most one rx channel (virtio eventq, P2A channel).

The following feature bit defined in [1] is not implemented:
VIRTIO_SCMI_F_SHARED_MEMORY.

After the preparatory patches, implement the virtio transport as
paraphrased:

Only support a single arm-scmi device (which is consistent with the SCMI
spec). Call scmi-virtio init from arm-scmi module init. During the
arm-scmi probing, link to the first probed scmi-virtio device. Defer
arm-scmi probing if no scmi-virtio device is bound yet.

Use the scmi_xfer tx/rx buffers for data exchange with the virtio device
in order to avoid redundant maintenance of additional buffers. Allocate
the buffers in the SCMI transport, and prepend room for a small header
used by the virtio transport to the tx/rx buffers.

For simplicity, restrict the number of messages which can be pending
simultaneously according to the virtqueue capacity. (The virtqueue sizes
are negotiated with the virtio device.)

As soon as rx channel message buffers are allocated or have been read
out by the arm-scmi driver, feed them to the virtio device.

Since some virtio devices may not have the short response time exhibited
by SCMI platforms using other transports, set a generous response
timeout.

Limitations:

Do not adjust the other SCMI timeouts for delayed response and polling
for now, since these timeouts are only relevant in special cases which
are not yet deemed relevant for this transport.

To do (as discussed in the cover letter):

- Avoid re-use of buffers still being used by the virtio device on
  timeouts.

- Avoid race conditions on receiving messages during/after channel free
  on driver probe failure or remove.

[1] https://lists.oasis-open.org/archives/virtio-comment/202005/msg00096.html
[2] https://www.oasis-open.org/committees/ballot.php?id=3496

Co-developed-by: Peter Hilber <peter.hilber@...nsynergy.com>
Signed-off-by: Peter Hilber <peter.hilber@...nsynergy.com>
Signed-off-by: Igor Skalkin <igor.skalkin@...nsynergy.com>
---
 MAINTAINERS                        |   1 +
 drivers/firmware/Kconfig           |  12 +-
 drivers/firmware/arm_scmi/Makefile |   1 +
 drivers/firmware/arm_scmi/common.h |  14 +
 drivers/firmware/arm_scmi/driver.c |  11 +
 drivers/firmware/arm_scmi/virtio.c | 493 +++++++++++++++++++++++++++++
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_scmi.h   |  41 +++
 8 files changed, 573 insertions(+), 1 deletion(-)
 create mode 100644 drivers/firmware/arm_scmi/virtio.c
 create mode 100644 include/uapi/linux/virtio_scmi.h

diff --git a/MAINTAINERS b/MAINTAINERS
index deaafb617361..8df73d6ddfc1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16772,6 +16772,7 @@ F:	drivers/firmware/arm_scpi.c
 F:	drivers/reset/reset-scmi.c
 F:	include/linux/sc[mp]i_protocol.h
 F:	include/trace/events/scmi.h
+F:	include/uapi/linux/virtio_scmi.h
 
 SYSTEM RESET/SHUTDOWN DRIVERS
 M:	Sebastian Reichel <sre@...nel.org>
diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index bdde51adb267..c4bdd84f7405 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -9,7 +9,7 @@ menu "Firmware Drivers"
 config ARM_SCMI_PROTOCOL
 	tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
 	depends on ARM || ARM64 || COMPILE_TEST
-	depends on ARM_SCMI_HAVE_SHMEM
+	depends on ARM_SCMI_HAVE_SHMEM || VIRTIO_SCMI
 	help
 	  ARM System Control and Management Interface (SCMI) protocol is a
 	  set of operating system-independent software interfaces that are
@@ -34,6 +34,16 @@ config ARM_SCMI_HAVE_SHMEM
 	  This declares whether a shared memory based transport for SCMI is
 	  available.
 
+config VIRTIO_SCMI
+	bool "Virtio transport for SCMI"
+	default n
+	depends on VIRTIO
+	help
+	  This enables the virtio based transport for SCMI.
+
+	  If you want to use the ARM SCMI protocol between the virtio guest and
+	  a host providing a virtio SCMI device, answer Y.
+
 config ARM_SCMI_POWER_DOMAIN
 	tristate "SCMI power domain driver"
 	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
index 3cc7fa40a464..25caea5e1969 100644
--- a/drivers/firmware/arm_scmi/Makefile
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -4,6 +4,7 @@ scmi-driver-y = driver.o notify.o
 scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
 scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
 scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
+scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
 scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o
 scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
 		    $(scmi-transport-y)
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 13c9ac176b23..b46dfe84e78b 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -165,6 +165,17 @@ int scmi_base_protocol_init(struct scmi_handle *h);
 int __init scmi_bus_init(void);
 void __exit scmi_bus_exit(void);
 
+#ifdef CONFIG_VIRTIO_SCMI
+int __init virtio_scmi_init(void);
+void __exit virtio_scmi_exit(void);
+#else
+static inline int __init virtio_scmi_init(void)
+{
+	return 0;
+}
+#define virtio_scmi_exit() do { } while (0)
+#endif
+
 #define DECLARE_SCMI_REGISTER_UNREGISTER(func)		\
 	int __init scmi_##func##_register(void);	\
 	void __exit scmi_##func##_unregister(void)
@@ -263,6 +274,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
 #ifdef CONFIG_HAVE_ARM_SMCCC
 extern const struct scmi_desc scmi_smc_desc;
 #endif
+#ifdef CONFIG_VIRTIO_SCMI
+extern const struct scmi_desc scmi_virtio_desc;
+#endif
 
 int scmi_set_transport_info(struct device *dev, void *transport_info);
 void *scmi_get_transport_info(struct device *dev);
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 244141e45e88..923ba526e829 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -996,6 +996,9 @@ static const struct of_device_id scmi_of_match[] = {
 #endif
 #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
 	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
+#endif
+#ifdef CONFIG_VIRTIO_SCMI
+	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
 #endif
 	{ /* Sentinel */ },
 };
@@ -1014,8 +1017,14 @@ static struct platform_driver scmi_driver = {
 
 static int __init scmi_driver_init(void)
 {
+	int ret;
+
 	scmi_bus_init();
 
+	ret = virtio_scmi_init();
+	if (ret)
+		return ret;
+
 	scmi_clock_register();
 	scmi_perf_register();
 	scmi_power_register();
@@ -1038,6 +1047,8 @@ static void __exit scmi_driver_exit(void)
 	scmi_sensors_unregister();
 	scmi_system_unregister();
 
+	virtio_scmi_exit();
+
 	platform_driver_unregister(&scmi_driver);
 }
 module_exit(scmi_driver_exit);
diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
new file mode 100644
index 000000000000..f70aa72f34f1
--- /dev/null
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -0,0 +1,493 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtio Transport driver for Arm System Control and Management Interface
+ * (SCMI).
+ *
+ * Copyright (C) 2020 OpenSynergy.
+ */
+
+/**
+ * DOC: Theory of Operation
+ *
+ * The scmi-virtio transport implements a driver for the virtio SCMI device
+ * proposed in virtio spec patch v5[1].
+ *
+ * There is one tx channel (virtio cmdq, A2P channel) and at most one rx
+ * channel (virtio eventq, P2A channel). Each channel is implemented through a
+ * virtqueue. Access to each virtqueue is protected by a spinlock.
+ *
+ * This SCMI transport uses the scmi_xfer tx/rx buffers for data exchange with
+ * the virtio device to avoid maintenance of additional buffers.
+ *
+ * [1] https://lists.oasis-open.org/archives/virtio-comment/202005/msg00096.html
+ */
+
+#include <linux/errno.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_scmi.h>
+
+#include "common.h"
+
+#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
+#define DESCR_PER_TX_MSG 2
+
+struct scmi_vio_channel {
+	spinlock_t lock;
+	struct virtqueue *vqueue;
+	struct scmi_chan_info *cinfo;
+	u8 is_rx;
+};
+
+union virtio_scmi_input {
+	__virtio32 hdr;
+	struct virtio_scmi_response response;
+	struct virtio_scmi_notification notification;
+};
+
+struct scmi_vio_msg {
+	struct virtio_scmi_request *request;
+	union virtio_scmi_input *input;
+	u8 completed;
+};
+
+static int scmi_vio_populate_vq_rx(struct scmi_vio_channel *vioch,
+				   struct scmi_xfer *xfer)
+{
+	struct scatterlist sg_in;
+	struct scmi_vio_msg *msg = xfer->extra_data;
+	int rc;
+
+	msg->completed = false;
+
+	sg_init_one(&sg_in, msg->input,
+		    sizeof(*msg->input) + VIRTIO_SCMI_MAX_MSG_SIZE);
+
+	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, xfer, GFP_ATOMIC);
+	if (rc)
+		dev_err(vioch->cinfo->dev, "%s() rc=%d\n", __func__, rc);
+	else
+		virtqueue_kick(vioch->vqueue);
+
+	return rc;
+}
+
+static void scmi_vio_complete_cb(struct virtqueue *vqueue)
+{
+	struct scmi_vio_channel *vioch = vqueue->priv;
+	unsigned long iflags;
+	unsigned int length;
+
+	spin_lock_irqsave(&vioch->lock, iflags);
+
+	do {
+		struct scmi_xfer *xfer;
+
+		virtqueue_disable_cb(vqueue);
+
+		while ((xfer = virtqueue_get_buf(vqueue, &length))) {
+			struct scmi_vio_msg *msg = xfer->extra_data;
+			u32 msg_hdr =
+				virtio32_to_cpu(vqueue->vdev, msg->input->hdr);
+			u8 msg_type = MSG_XTRACT_TYPE(msg_hdr);
+
+			if (!vioch->is_rx) { /* tx queue response */
+				msg->completed = true;
+				xfer->rx.len =
+					length - sizeof(msg->input->response);
+				if (!xfer->hdr.poll_completion)
+					scmi_rx_callback(vioch->cinfo, msg_hdr);
+				continue;
+			}
+
+			/* rx queue - notification or delayed response */
+			switch (msg_type) {
+			case MSG_TYPE_NOTIFICATION:
+				xfer->rx.len = length -
+					       sizeof(msg->input->notification);
+				xfer->rx.buf = msg->input->notification.data;
+				break;
+			case MSG_TYPE_DELAYED_RESP:
+				xfer->rx.len =
+					length - sizeof(msg->input->response);
+				xfer->rx.buf = msg->input->response.data;
+				break;
+			default:
+				dev_warn_once(vioch->cinfo->dev,
+					      "rx: unknown message_type %d\n",
+					      msg_type);
+				scmi_vio_populate_vq_rx(vioch, xfer);
+				continue;
+			}
+
+			scmi_rx_callback(vioch->cinfo, msg_hdr);
+			scmi_vio_populate_vq_rx(vioch, xfer);
+		}
+
+		if (unlikely(virtqueue_is_broken(vqueue)))
+			break;
+	} while (!virtqueue_enable_cb(vqueue));
+
+	spin_unlock_irqrestore(&vioch->lock, iflags);
+}
+
+static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
+
+static vq_callback_t *scmi_vio_complete_callbacks[] = {
+	scmi_vio_complete_cb,
+	scmi_vio_complete_cb
+};
+
+static int scmi_vio_match_any_dev(struct device *dev, const void *data)
+{
+	(void)dev;
+	(void)data;
+
+	return 1;
+}
+
+static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
+
+static int virtio_link_supplier(struct device *dev)
+{
+	struct device *vdev = driver_find_device(
+		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
+
+	if (!vdev) {
+		dev_notice_once(
+			dev,
+			"Deferring probe after not finding a bound scmi-virtio device\n");
+		return -EPROBE_DEFER;
+	}
+
+	/*
+	 * Add plain device link for completeness. It might have no effect
+	 * beyond sysfs.
+	 */
+	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
+		put_device(vdev);
+		dev_err(dev, "Adding link to supplier virtio device failed\n");
+		return -ECANCELED;
+	}
+
+	put_device(vdev);
+	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
+}
+
+static bool virtio_chan_available(struct device *dev, int idx)
+{
+	struct virtio_device *vdev;
+	struct scmi_vio_channel **vioch;
+
+	/* scmi-virtio doesn't support per-protocol channels */
+	if (is_scmi_protocol_device(dev))
+		return false;
+
+	vdev = scmi_get_transport_info(dev);
+	if (!vdev)
+		return false;
+
+	vioch = vdev->priv;
+	if (!vioch)
+		return false;
+
+	return vioch[idx] && vioch[idx]->vqueue;
+}
+
+static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
+			     bool tx)
+{
+	struct virtio_device *vdev;
+	struct scmi_vio_channel **vioch;
+	int vioch_index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
+
+	/* scmi-virtio doesn't support per-protocol channels */
+	if (is_scmi_protocol_device(dev))
+		return -1;
+
+	vdev = scmi_get_transport_info(dev);
+	if (!vdev)
+		return -1;
+
+	vioch = vdev->priv;
+	if (!vioch) {
+		dev_err(dev, "Data from scmi-virtio probe not found\n");
+		return -1;
+	}
+	cinfo->transport_info = vioch[vioch_index];
+	vioch[vioch_index]->cinfo = cinfo;
+
+	return 0;
+}
+
+static int virtio_chan_free(int id, void *p, void *data)
+{
+	struct scmi_chan_info *cinfo = p;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+	if (vioch) {
+		cinfo->transport_info = NULL;
+		kfree(vioch);
+	}
+
+	scmi_free_channel(cinfo, data, id);
+	return 0;
+}
+
+static int virtio_get_max_msg(bool tx, struct scmi_chan_info *base_cinfo,
+			      int *max_msg)
+{
+	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
+
+	*max_msg = virtqueue_get_vring_size(vioch->vqueue);
+
+	/* Tx messages need multiple descriptors. */
+	if (tx)
+		*max_msg /= DESCR_PER_TX_MSG;
+
+	if (*max_msg > MSG_TOKEN_MAX) {
+		dev_notice(
+			base_cinfo->dev,
+			"Only %ld messages can be pending simultaneously, while the virtqueue could hold %d\n",
+			MSG_TOKEN_MAX, *max_msg);
+		*max_msg = MSG_TOKEN_MAX;
+	}
+
+	return 0;
+}
+
+static int virtio_xfer_init_buffers(struct scmi_chan_info *cinfo,
+				    struct scmi_xfer *xfer, int max_msg_size)
+{
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scmi_vio_msg *msg;
+
+	msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	xfer->extra_data = msg;
+
+	if (vioch->is_rx) {
+		int rc;
+		unsigned long iflags;
+
+		msg->input = devm_kzalloc(cinfo->dev,
+					  sizeof(*msg->input) + max_msg_size,
+					  GFP_KERNEL);
+		if (!msg->input)
+			return -ENOMEM;
+
+		/*
+		 * xfer->rx.buf will be set to notification or delayed response
+		 * specific values in the receive callback, according to the
+		 * type of the received message.
+		 */
+
+		spin_lock_irqsave(&vioch->lock, iflags);
+		rc = scmi_vio_populate_vq_rx(vioch, xfer);
+		spin_unlock_irqrestore(&vioch->lock, iflags);
+		if (rc)
+			return rc;
+	} else {
+		msg->request =
+			devm_kzalloc(cinfo->dev,
+				     sizeof(*msg->request) + max_msg_size,
+				     GFP_KERNEL);
+		if (!msg->request)
+			return -ENOMEM;
+
+		xfer->tx.buf = msg->request->data;
+
+		msg->input = devm_kzalloc(
+			cinfo->dev, sizeof(msg->input->response) + max_msg_size,
+			GFP_KERNEL);
+		if (!msg->input)
+			return -ENOMEM;
+
+		xfer->rx.buf = msg->input->response.data;
+	}
+
+	return 0;
+}
+
+static int scmi_vio_send(struct scmi_vio_channel *vioch, struct scmi_xfer *xfer)
+{
+	struct scatterlist sg_out;
+	struct scatterlist sg_in;
+	struct scatterlist *sgs[DESCR_PER_TX_MSG] = { &sg_out, &sg_in };
+	struct scmi_vio_msg *msg = xfer->extra_data;
+	unsigned long iflags;
+	int rc;
+
+	msg->completed = false;
+
+	sg_init_one(&sg_out, msg->request,
+		    sizeof(*msg->request) + xfer->tx.len);
+	sg_init_one(&sg_in, &msg->input->response,
+		    sizeof(msg->input->response) + xfer->rx.len);
+
+	spin_lock_irqsave(&vioch->lock, iflags);
+	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, xfer, GFP_ATOMIC);
+	if (rc)
+		dev_err(vioch->cinfo->dev, "%s() rc=%d\n", __func__, rc);
+	else
+		virtqueue_kick(vioch->vqueue);
+	spin_unlock_irqrestore(&vioch->lock, iflags);
+
+	return rc;
+}
+
+static int virtio_send_message(struct scmi_chan_info *cinfo,
+			       struct scmi_xfer *xfer)
+{
+	uint32_t hdr;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct virtio_device *vdev = vioch->vqueue->vdev;
+	struct scmi_vio_msg *msg = xfer->extra_data;
+
+	hdr = pack_scmi_header(&xfer->hdr);
+
+	msg->request->hdr = cpu_to_virtio32(vdev, hdr);
+
+	return scmi_vio_send(vioch, xfer);
+}
+
+static void virtio_fetch_response(struct scmi_chan_info *cinfo,
+				  struct scmi_xfer *xfer)
+{
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scmi_vio_msg *msg = xfer->extra_data;
+
+	xfer->hdr.status = virtio32_to_cpu(vioch->vqueue->vdev,
+					   msg->input->response.status);
+}
+
+static void dummy_fetch_notification(struct scmi_chan_info *cinfo,
+				     size_t max_len, struct scmi_xfer *xfer)
+{
+	(void)cinfo;
+	(void)max_len;
+	(void)xfer;
+}
+
+static void dummy_clear_channel(struct scmi_chan_info *cinfo)
+{
+	(void)cinfo;
+}
+
+static bool virtio_poll_done(struct scmi_chan_info *cinfo,
+			     struct scmi_xfer *xfer)
+{
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scmi_vio_msg *msg = xfer->extra_data;
+	unsigned long iflags;
+	bool completed;
+
+	spin_lock_irqsave(&vioch->lock, iflags);
+	completed = msg->completed;
+	spin_unlock_irqrestore(&vioch->lock, iflags);
+
+	return completed;
+}
+
+static const struct scmi_transport_ops scmi_virtio_ops = {
+	.link_supplier = virtio_link_supplier,
+	.chan_available = virtio_chan_available,
+	.chan_setup = virtio_chan_setup,
+	.chan_free = virtio_chan_free,
+	.get_max_msg = virtio_get_max_msg,
+	.send_message = virtio_send_message,
+	.fetch_response = virtio_fetch_response,
+	.fetch_notification = dummy_fetch_notification,
+	.clear_channel = dummy_clear_channel,
+	.poll_done = virtio_poll_done,
+	.xfer_init_buffers = virtio_xfer_init_buffers,
+};
+
+const struct scmi_desc scmi_virtio_desc = {
+	.ops = &scmi_virtio_ops,
+	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
+	.max_msg = 0, /* overridden by virtio_get_max_msg() */
+	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+};
+
+static int scmi_vio_probe(struct virtio_device *vdev)
+{
+	struct device *dev = &vdev->dev;
+	struct scmi_vio_channel **vioch;
+	bool have_vq_rx;
+	int vq_cnt;
+	int i;
+	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
+
+	vioch = devm_kcalloc(dev, VIRTIO_SCMI_VQ_MAX_CNT, sizeof(*vioch),
+			     GFP_KERNEL);
+	if (!vioch)
+		return -ENOMEM;
+
+	have_vq_rx = virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
+	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
+
+	for (i = 0; i < vq_cnt; i++) {
+		vioch[i] = devm_kzalloc(dev, sizeof(**vioch), GFP_KERNEL);
+		if (!vioch[i])
+			return -ENOMEM;
+	}
+
+	if (have_vq_rx)
+		vioch[VIRTIO_SCMI_VQ_RX]->is_rx = true;
+
+	if (virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
+			    scmi_vio_vqueue_names, NULL)) {
+		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
+		return -1;
+	}
+	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
+
+	for (i = 0; i < vq_cnt; i++) {
+		spin_lock_init(&vioch[i]->lock);
+		vioch[i]->vqueue = vqs[i];
+		vioch[i]->vqueue->priv = vioch[i];
+	}
+
+	vdev->priv = vioch;
+
+	virtio_device_ready(vdev);
+
+	return 0;
+}
+
+static unsigned int features[] = {
+	VIRTIO_SCMI_F_P2A_CHANNELS,
+};
+
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
+	{ 0 }
+};
+
+static struct virtio_driver virtio_scmi_driver = {
+	.driver.name = "scmi-virtio",
+	.driver.owner = THIS_MODULE,
+	.feature_table = features,
+	.feature_table_size = ARRAY_SIZE(features),
+	.id_table = id_table,
+	.probe = scmi_vio_probe,
+};
+
+int __init virtio_scmi_init(void)
+{
+	return register_virtio_driver(&virtio_scmi_driver);
+}
+
+void __exit virtio_scmi_exit(void)
+{
+	unregister_virtio_driver(&virtio_scmi_driver);
+}
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index b052355ac7a3..57d233c02720 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -48,5 +48,6 @@
 #define VIRTIO_ID_FS           26 /* virtio filesystem */
 #define VIRTIO_ID_PMEM         27 /* virtio pmem */
 #define VIRTIO_ID_MAC80211_HWSIM 29 /* virtio mac80211-hwsim */
+#define VIRTIO_ID_SCMI         32 /* virtio SCMI */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
new file mode 100644
index 000000000000..9f21b3dbbfe2
--- /dev/null
+++ b/include/uapi/linux/virtio_scmi.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
+/*
+ * Copyright (C) 2020 OpenSynergy GmbH
+ */
+
+#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
+#define _UAPI_LINUX_VIRTIO_SCMI_H
+
+#include <linux/virtio_types.h>
+
+/* Feature bits */
+
+/* Device implements some SCMI notifications, or delayed responses. */
+#define VIRTIO_SCMI_F_P2A_CHANNELS 0
+
+/* Device implements any SCMI statistics shared memory region */
+#define VIRTIO_SCMI_F_SHARED_MEMORY 1
+
+/* Virtqueues */
+
+#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
+#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
+#define VIRTIO_SCMI_VQ_MAX_CNT 2
+
+struct virtio_scmi_request {
+	__virtio32 hdr;
+	__u8 data[];
+};
+
+struct virtio_scmi_response {
+	__virtio32 hdr;
+	__virtio32 status;
+	__u8 data[];
+};
+
+struct virtio_scmi_notification {
+	__virtio32 hdr;
+	__u8 data[];
+};
+
+#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
-- 
2.25.1

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