firmware: arm_scmi: Make VirtIO transport a standalone driver

Make SCMI VirtIO transport a standalone driver that can be optionally
loaded as a module.

CC: Michael S. Tsirkin <mst@redhat.com>
CC: Igor Skalkin <igor.skalkin@opensynergy.com>
CC: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20240812173340.3912830-9-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/Kconfig

@@ -71,47 +71,6 @@ config ARM_SCMI_DEBUG_COUNTERS
 
 source "drivers/firmware/arm_scmi/transports/Kconfig"
 
-config ARM_SCMI_TRANSPORT_VIRTIO
-	bool "SCMI transport based on VirtIO"
-	depends on VIRTIO=y || VIRTIO=ARM_SCMI_PROTOCOL
-	select ARM_SCMI_HAVE_TRANSPORT
-	select ARM_SCMI_HAVE_MSG
-	help
-	  This enables the virtio based transport for SCMI.
-
-	  If you want the ARM SCMI PROTOCOL stack to include support for a
-	  transport based on VirtIO, answer Y.
-
-config ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
-	bool "SCMI VirtIO transport Version 1 compliance"
-	depends on ARM_SCMI_TRANSPORT_VIRTIO
-	default y
-	help
-	  This enforces strict compliance with VirtIO Version 1 specification.
-
-	  If you want the ARM SCMI VirtIO transport layer to refuse to work
-	  with Legacy VirtIO backends and instead support only VirtIO Version 1
-	  devices (or above), answer Y.
-
-	  If you want instead to support also old Legacy VirtIO backends (like
-	  the ones implemented by kvmtool) and let the core Kernel VirtIO layer
-	  take care of the needed conversions, say N.
-
-config ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE
-	bool "Enable atomic mode for SCMI VirtIO transport"
-	depends on ARM_SCMI_TRANSPORT_VIRTIO
-	help
-	  Enable support of atomic operation for SCMI VirtIO based transport.
-
-	  If you want the SCMI VirtIO based transport to operate in atomic
-	  mode, avoiding any kind of sleeping behaviour for selected
-	  transactions on the TX path, answer Y.
-
-	  Enabling atomic mode operations allows any SCMI driver using this
-	  transport to optionally ask for atomic SCMI transactions and operate
-	  in atomic context too, at the price of using a number of busy-waiting
-	  primitives all over instead. If unsure say N.
-
 endif #ARM_SCMI_PROTOCOL
 
 config ARM_SCMI_POWER_CONTROL

drivers/firmware/arm_scmi/Makefile

@@ -6,7 +6,6 @@ scmi-driver-y = driver.o notify.o
 scmi-driver-$(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT) += raw_mode.o
 scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
 scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
-scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO) += virtio.o
 scmi-protocols-y := base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o powercap.o
 scmi-protocols-y += pinctrl.o
 scmi-module-objs := $(scmi-driver-y) $(scmi-protocols-y) $(scmi-transport-y)

drivers/firmware/arm_scmi/common.h

@@ -286,9 +286,6 @@ int scmi_xfer_raw_inflight_register(const struct scmi_handle *handle,
 int scmi_xfer_raw_wait_for_message_response(struct scmi_chan_info *cinfo,
 					    struct scmi_xfer *xfer,
 					    unsigned int timeout_ms);
-#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
-extern const struct scmi_desc scmi_virtio_desc;
-#endif
 
 void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr, void *priv);
 

drivers/firmware/arm_scmi/driver.c

@@ -3318,9 +3318,6 @@ ATTRIBUTE_GROUPS(versions);
 
 /* Each compatible listed below must have descriptor associated with it */
 static const struct of_device_id scmi_of_match[] = {
-#ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
-	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
-#endif
 	{ /* Sentinel */ },
 };
 

drivers/firmware/arm_scmi/transports/Kconfig

@@ -77,4 +77,47 @@ config ARM_SCMI_TRANSPORT_OPTEE
 	  This driver can also be built as a module. If so, the module
 	  will be called scmi_transport_optee.
 
+config ARM_SCMI_TRANSPORT_VIRTIO
+	tristate "SCMI transport based on VirtIO"
+	depends on VIRTIO
+	select ARM_SCMI_HAVE_TRANSPORT
+	select ARM_SCMI_HAVE_MSG
+	help
+	  This enables the virtio based transport for SCMI.
+
+	  If you want the ARM SCMI PROTOCOL stack to include support for a
+	  transport based on VirtIO, answer Y.
+	  This driver can also be built as a module. If so, the module
+	  will be called scmi_transport_virtio.
+
+config ARM_SCMI_TRANSPORT_VIRTIO_VERSION1_COMPLIANCE
+	bool "SCMI VirtIO transport Version 1 compliance"
+	depends on ARM_SCMI_TRANSPORT_VIRTIO
+	default y
+	help
+	  This enforces strict compliance with VirtIO Version 1 specification.
+
+	  If you want the ARM SCMI VirtIO transport layer to refuse to work
+	  with Legacy VirtIO backends and instead support only VirtIO Version 1
+	  devices (or above), answer Y.
+
+	  If you want instead to support also old Legacy VirtIO backends (like
+	  the ones implemented by kvmtool) and let the core Kernel VirtIO layer
+	  take care of the needed conversions, say N.
+
+config ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE
+	bool "Enable atomic mode for SCMI VirtIO transport"
+	depends on ARM_SCMI_TRANSPORT_VIRTIO
+	help
+	  Enable support of atomic operation for SCMI VirtIO based transport.
+
+	  If you want the SCMI VirtIO based transport to operate in atomic
+	  mode, avoiding any kind of sleeping behaviour for selected
+	  transactions on the TX path, answer Y.
+
+	  Enabling atomic mode operations allows any SCMI driver using this
+	  transport to optionally ask for atomic SCMI transactions and operate
+	  in atomic context too, at the price of using a number of busy-waiting
+	  primitives all over instead. If unsure say N.
+
 endmenu

drivers/firmware/arm_scmi/transports/Makefile

@@ -5,6 +5,8 @@ scmi_transport_smc-objs := smc.o
 obj-$(CONFIG_ARM_SCMI_TRANSPORT_SMC) += scmi_transport_smc.o
 scmi_transport_optee-objs := optee.o
 obj-$(CONFIG_ARM_SCMI_TRANSPORT_OPTEE) += scmi_transport_optee.o
+scmi_transport_virtio-objs := virtio.o
+obj-$(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO) += scmi_transport_virtio.o
 
 ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy)
 # The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame

drivers/firmware/arm_scmi/virtio.c → drivers/firmware/arm_scmi/transports/virtio.c

@@ -4,7 +4,7 @@
  * (SCMI).
  *
  * Copyright (C) 2020-2022 OpenSynergy.
- * Copyright (C) 2021-2022 ARM Ltd.
+ * Copyright (C) 2021-2024 ARM Ltd.
  */
 
 /**
@@ -19,6 +19,7 @@
 
 #include <linux/completion.h>
 #include <linux/errno.h>
+#include <linux/platform_device.h>
 #include <linux/refcount.h>
 #include <linux/slab.h>
 #include <linux/virtio.h>
@@ -27,7 +28,7 @@
 #include <uapi/linux/virtio_ids.h>
 #include <uapi/linux/virtio_scmi.h>
 
-#include "common.h"
+#include "../common.h"
 
 #define VIRTIO_MAX_RX_TIMEOUT_MS	60000
 #define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
@@ -108,6 +109,8 @@ struct scmi_vio_msg {
 	refcount_t users;
 };
 
+static struct scmi_transport_core_operations *core;
+
 /* Only one SCMI VirtIO device can possibly exist */
 static struct virtio_device *scmi_vdev;
 
@@ -294,8 +297,9 @@ static void scmi_vio_complete_cb(struct virtqueue *vqueue)
 
 		if (msg) {
 			msg->rx_len = length;
-			scmi_rx_callback(vioch->cinfo,
-					 scmi_msg_ops.read_header(msg->input), msg);
+			core->rx_callback(vioch->cinfo,
+					  core->msg->read_header(msg->input),
+					  msg);
 
 			scmi_finalize_message(vioch, msg);
 		}
@@ -339,8 +343,9 @@ static void scmi_vio_deferred_tx_worker(struct work_struct *work)
 		 * is no more processed elsewhere so no poll_lock needed.
 		 */
 		if (msg->poll_status == VIO_MSG_NOT_POLLED)
-			scmi_rx_callback(vioch->cinfo,
-					 scmi_msg_ops.read_header(msg->input), msg);
+			core->rx_callback(vioch->cinfo,
+					  core->msg->read_header(msg->input),
+					  msg);
 
 		/* Free the processed message once done */
 		scmi_vio_msg_release(vioch, msg);
@@ -366,23 +371,6 @@ static unsigned int virtio_get_max_msg(struct scmi_chan_info *base_cinfo)
 	return vioch->max_msg;
 }
 
-static int virtio_link_supplier(struct device *dev)
-{
-	if (!scmi_vdev) {
-		dev_notice(dev,
-			   "Deferring probe after not finding a bound scmi-virtio device\n");
-		return -EPROBE_DEFER;
-	}
-
-	if (!device_link_add(dev, &scmi_vdev->dev,
-			     DL_FLAG_AUTOREMOVE_CONSUMER)) {
-		dev_err(dev, "Adding link to supplier virtio device failed\n");
-		return -ECANCELED;
-	}
-
-	return 0;
-}
-
 static bool virtio_chan_available(struct device_node *of_node, int idx)
 {
 	struct scmi_vio_channel *channels, *vioch = NULL;
@@ -510,10 +498,10 @@ static int virtio_send_message(struct scmi_chan_info *cinfo,
 		return -EBUSY;
 	}
 
-	scmi_msg_ops.tx_prepare(msg->request, xfer);
+	core->msg->tx_prepare(msg->request, xfer);
 
-	sg_init_one(&sg_out, msg->request, scmi_msg_ops.command_size(xfer));
-	sg_init_one(&sg_in, msg->input, scmi_msg_ops.response_size(xfer));
+	sg_init_one(&sg_out, msg->request, core->msg->command_size(xfer));
+	sg_init_one(&sg_in, msg->input, core->msg->response_size(xfer));
 
 	spin_lock_irqsave(&vioch->lock, flags);
 
@@ -560,7 +548,7 @@ static void virtio_fetch_response(struct scmi_chan_info *cinfo,
 	struct scmi_vio_msg *msg = xfer->priv;
 
 	if (msg)
-		scmi_msg_ops.fetch_response(msg->input, msg->rx_len, xfer);
+		core->msg->fetch_response(msg->input, msg->rx_len, xfer);
 }
 
 static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
@@ -569,7 +557,8 @@ static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
 	struct scmi_vio_msg *msg = xfer->priv;
 
 	if (msg)
-		scmi_msg_ops.fetch_notification(msg->input, msg->rx_len, max_len, xfer);
+		core->msg->fetch_notification(msg->input, msg->rx_len,
+					      max_len, xfer);
 }
 
 /**
@@ -669,7 +658,7 @@ static void virtio_mark_txdone(struct scmi_chan_info *cinfo, int ret,
  * the message we are polling for could be alternatively delivered via usual
  * IRQs callbacks on another core which happened to have IRQs enabled while we
  * are actively polling for it here: in such a case it will be handled as such
- * by scmi_rx_callback() and the polling loop in the SCMI Core TX path will be
+ * by rx_callback() and the polling loop in the SCMI Core TX path will be
  * transparently terminated anyway.
  *
  * Return: True once polling has successfully completed.
@@ -790,7 +779,6 @@ static bool virtio_poll_done(struct scmi_chan_info *cinfo,
 }
 
 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,
@@ -802,6 +790,23 @@ static const struct scmi_transport_ops scmi_virtio_ops = {
 	.poll_done = virtio_poll_done,
 };
 
+static const struct scmi_desc scmi_virtio_desc = {
+	.ops = &scmi_virtio_ops,
+	/* for non-realtime virtio devices */
+	.max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
+	.max_msg = 0, /* overridden by virtio_get_max_msg() */
+	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+	.atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
+};
+
+static const struct of_device_id scmi_of_match[] = {
+	{ .compatible = "arm,scmi-virtio" },
+	{ /* Sentinel */ },
+};
+
+DEFINE_SCMI_TRANSPORT_DRIVER(scmi_virtio, scmi_virtio_driver, scmi_virtio_desc,
+			     scmi_of_match, core);
+
 static int scmi_vio_probe(struct virtio_device *vdev)
 {
 	struct device *dev = &vdev->dev;
@@ -861,14 +866,27 @@ static int scmi_vio_probe(struct virtio_device *vdev)
 	}
 
 	vdev->priv = channels;
+
 	/* Ensure initialized scmi_vdev is visible */
 	smp_store_mb(scmi_vdev, vdev);
 
+	ret = platform_driver_register(&scmi_virtio_driver);
+	if (ret) {
+		vdev->priv = NULL;
+		vdev->config->del_vqs(vdev);
+		/* Ensure NULLified scmi_vdev is visible */
+		smp_store_mb(scmi_vdev, NULL);
+
+		return ret;
+	}
+
 	return 0;
 }
 
 static void scmi_vio_remove(struct virtio_device *vdev)
 {
+	platform_driver_unregister(&scmi_virtio_driver);
+
 	/*
 	 * Once we get here, virtio_chan_free() will have already been called by
 	 * the SCMI core for any existing channel and, as a consequence, all the
@@ -913,23 +931,10 @@ static struct virtio_driver virtio_scmi_driver = {
 	.validate = scmi_vio_validate,
 };
 
-static int __init virtio_scmi_init(void)
-{
-	return register_virtio_driver(&virtio_scmi_driver);
-}
-
-static void virtio_scmi_exit(void)
-{
-	unregister_virtio_driver(&virtio_scmi_driver);
-}
+module_virtio_driver(virtio_scmi_driver);
 
-const struct scmi_desc scmi_virtio_desc = {
-	.transport_init = virtio_scmi_init,
-	.transport_exit = virtio_scmi_exit,
-	.ops = &scmi_virtio_ops,
-	/* for non-realtime virtio devices */
-	.max_rx_timeout_ms = VIRTIO_MAX_RX_TIMEOUT_MS,
-	.max_msg = 0, /* overridden by virtio_get_max_msg() */
-	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
-	.atomic_enabled = IS_ENABLED(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO_ATOMIC_ENABLE),
-};
+MODULE_AUTHOR("Igor Skalkin <igor.skalkin@opensynergy.com>");
+MODULE_AUTHOR("Peter Hilber <peter.hilber@opensynergy.com>");
+MODULE_AUTHOR("Cristian Marussi <cristian.marussi@arm.com>");
+MODULE_DESCRIPTION("SCMI VirtIO Transport driver");
+MODULE_LICENSE("GPL");