path: root/drivers/firmware/arm_scmi/virtio.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Virtio Transport driver for Arm System Control and Management Interface
 * (SCMI).
 *
 * Copyright (C) 2020-2022 OpenSynergy.
 * Copyright (C) 2021-2022 ARM Ltd.
 */

/**
 * DOC: Theory of Operation
 *
 * The scmi-virtio transport implements a driver for the virtio SCMI device.
 *
 * 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 spinlocks.
 */

#include <linux/completion.h>
#include <linux/errno.h>
#include <linux/refcount.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_MAX_RX_TIMEOUT_MS	60000
#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
#define VIRTIO_SCMI_MAX_PDU_SIZE \
	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
#define DESCRIPTORS_PER_TX_MSG 2

/**
 * struct scmi_vio_channel - Transport channel information
 *
 * @vqueue: Associated virtqueue
 * @cinfo: SCMI Tx or Rx channel
 * @free_lock: Protects access to the @free_list.
 * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
 * @deferred_tx_work: Worker for TX deferred replies processing
 * @deferred_tx_wq: Workqueue for TX deferred replies
 * @pending_lock: Protects access to the @pending_cmds_list.
 * @pending_cmds_list: List of pre-fetched commands queueud for later processing
 * @is_rx: Whether channel is an Rx channel
 * @max_msg: Maximum number of pending messages for this channel.
 * @lock: Protects access to all members except users, free_list and
 *	  pending_cmds_list.
 * @shutdown_done: A reference to a completion used when freeing this channel.
 * @users: A reference count to currently active users of this channel.
 */
struct scmi_vio_channel {
	struct virtqueue *vqueue;
	struct scmi_chan_info *cinfo;
	/* lock to protect access to the free list. */
	spinlock_t free_lock;
	struct list_head free_list;
	/* lock to protect access to the pending list. */
	spinlock_t pending_lock;
	struct list_head pending_cmds_list;
	struct work_struct deferred_tx_work;
	struct workqueue_struct *deferred_tx_wq;
	bool is_rx;
	unsigned int max_msg;
	/*
	 * Lock to protect access to all members except users, free_list and
	 * pending_cmds_list
	 */
	spinlock_t lock;
	struct completion *shutdown_done;
	refcount_t users;
};

enum poll_states {
	VIO_MSG_NOT_POLLED,
	VIO_MSG_POLL_TIMEOUT,
	VIO_MSG_POLLING,
	VIO_MSG_POLL_DONE,
};

/**
 * struct scmi_vio_msg - Transport PDU information
 *
 * @request: SDU used for commands
 * @input: SDU used for (delayed) responses and notifications
 * @list: List which scmi_vio_msg may be part of
 * @rx_len: Input SDU size in bytes, once input has been received
 * @poll_idx: Last used index registered for polling purposes if this message
 *	      transaction reply was configured for polling.
 * @poll_status: Polling state for this message.
 * @poll_lock: A lock to protect @poll_status
 * @users: A reference count to track this message users and avoid premature
 *	   freeing (and reuse) when polling and IRQ execution paths interleave.
 */
struct scmi_vio_msg {
	struct scmi_msg_payld *request;
	struct scmi_msg_payld *input;
	struct list_head list;
	unsigned int rx_len;
	unsigned int poll_idx;
	enum poll_states poll_status;
	/* Lock to protect access to poll_status */
	spinlock_t poll_lock;
	refcount_t users;
};

/* Only one SCMI VirtIO device can possibly exist */
static struct virtio_device *scmi_vdev;

static void scmi_vio_channel_ready(struct scmi_vio_channel *vioch,
				   struct scmi_chan_info *cinfo)
{
	unsigned long flags;

	spin_lock_irqsave(&vioch->lock, flags);
	cinfo->transport_info = vioch;
	/* Indirectly setting channel not available any more */
	vioch->cinfo = cinfo;
	spin_unlock_irqrestore(&vioch->lock, flags);

	refcount_set(&vioch->users, 1);
}

static inline bool scmi_vio_channel_acquire(struct scmi_vio_channel *vioch)
{
	return refcount_inc_not_zero(&vioch->users);
}

static inline void scmi_vio_channel_release(struct scmi_vio_channel *vioch)
{
	if (refcount_dec_and_test(&vioch->users)) {
		unsigned long flags;

		spin_lock_irqsave(&vioch->lock, flags);
		if (vioch->shutdown_done) {
			vioch->cinfo = NULL;
			complete(vioch->shutdown_done);
		}
		spin_unlock_irqrestore(&vioch->lock, flags);
	}
}

static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
{
	unsigned long flags;
	DECLARE_COMPLETION_ONSTACK(vioch_shutdown_done);
	void *deferred_wq = NULL;

	/*
	 * Prepare to wait for the last release if not already released
	 * or in progress.
	 */
	spin_lock_irqsave(&vioch->lock, flags);
	if (!vioch->cinfo || vioch->shutdown_done) {
		spin_unlock_irqrestore(&vioch->lock, flags);
		return;
	}

	vioch->shutdown_done = &vioch_shutdown_done;
	virtio_break_device(vioch->vqueue->vdev);
	if (!vioch->is_rx && vioch->deferred_tx_wq) {
		deferred_wq = vioch->deferred_tx_wq;
		/* Cannot be kicked anymore after this...*/
		vioch->deferred_tx_wq = NULL;
	}
	spin_unlock_irqrestore(&vioch->lock, flags);

	if (deferred_wq)
		destroy_workqueue(deferred_wq);

	scmi_vio_channel_release(vioch);

	/* Let any possibly concurrent RX path release the channel */
	wait_for_completion(vioch->shutdown_done);
}

/* Assumes to be called with vio channel acquired already */
static struct scmi_vio_msg *
scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
{
	unsigned long flags;
	struct scmi_vio_msg *msg;

	spin_lock_irqsave(&vioch->free_lock, flags);
	if (list_empty(&vioch->free_list)) {
		spin_unlock_irqrestore(&vioch->free_lock, flags);
		return NULL;
	}

	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
	list_del_init(&msg->list);
	spin_unlock_irqrestore(&vioch->free_lock, flags);

	/* Still no users, no need to acquire poll_lock */
	msg->poll_status = VIO_MSG_NOT_POLLED;
	refcount_set(&msg->users, 1);

	return msg;
}

static inline bool scmi_vio_msg_acquire(struct scmi_vio_msg *msg)
{
	return refcount_inc_not_zero(&msg->users);
}

/* Assumes to be called with vio channel acquired already */
static inline bool scmi_vio_msg_release(struct scmi_vio_channel *vioch,
					struct scmi_vio_msg *msg)
{
	bool ret;

	ret = refcount_dec_and_test(&msg->users);
	if (ret) {
		unsigned long flags;

		spin_lock_irqsave(&vioch->free_lock, flags);
		list_add_tail(&msg->list, &vioch->free_list);
		spin_unlock_irqrestore(&vioch->free_lock, flags);
	}

	return ret;
}

static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
{
	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
}

static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
			       struct scmi_vio_msg *msg)
{
	struct scatterlist sg_in;
	int rc;
	unsigned long flags;
	struct device *dev = &vioch->vqueue->vdev->dev;

	sg_init_one(&sg_in