vdpa/mlx5: map doorbell

The HW supports only 4 bytes doorbell writing detection.
The virtio device set only 2 bytes when it rings the doorbell.

Map the virtio doorbell detected by the virtio queue kickfd to the HW
VAR space when it expects to get the virtio emulation doorbell.

Use the EAL interrupt mechanism to get notification when a new event
appears in kickfd by the guest and write 4 bytes to the HW doorbell space
in the notification callback.

Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>

drivers/vdpa/mlx5/mlx5_vdpa.h

@@ -81,6 +81,7 @@ struct mlx5_vdpa_virtq {
 		void *buf;
 		uint32_t size;
 	} umems[3];
+	struct rte_intr_handle intr_handle;
 };
 
 struct mlx5_vdpa_steer {
@@ -118,6 +119,8 @@ struct mlx5_vdpa_priv {
 	uint16_t log_max_rqt_size;
 	SLIST_HEAD(virtq_list, mlx5_vdpa_virtq) virtq_list;
 	struct mlx5_vdpa_steer steer;
+	struct mlx5dv_var *var;
+	void *virtq_db_addr;
 	SLIST_HEAD(mr_list, mlx5_vdpa_query_mr) mr_list;
 };
 

drivers/vdpa/mlx5/mlx5_vdpa_virtq.c

@@ -2,9 +2,12 @@
  * Copyright 2019 Mellanox Technologies, Ltd
  */
 #include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
 
 #include <rte_malloc.h>
 #include <rte_errno.h>
+#include <rte_io.h>
 
 #include <mlx5_common.h>
 
@@ -12,11 +15,52 @@
 #include "mlx5_vdpa.h"
 
 
+static void
+mlx5_vdpa_virtq_handler(void *cb_arg)
+{
+	struct mlx5_vdpa_virtq *virtq = cb_arg;
+	struct mlx5_vdpa_priv *priv = virtq->priv;
+	uint64_t buf;
+	int nbytes;
+
+	do {
+		nbytes = read(virtq->intr_handle.fd, &buf, 8);
+		if (nbytes < 0) {
+			if (errno == EINTR ||
+			    errno == EWOULDBLOCK ||
+			    errno == EAGAIN)
+				continue;
+			DRV_LOG(ERR,  "Failed to read kickfd of virtq %d: %s",
+				virtq->index, strerror(errno));
+		}
+		break;
+	} while (1);
+	rte_write32(virtq->index, priv->virtq_db_addr);
+	DRV_LOG(DEBUG, "Ring virtq %u doorbell.", virtq->index);
+}
+
 static int
 mlx5_vdpa_virtq_unset(struct mlx5_vdpa_virtq *virtq)
 {
 	unsigned int i;
+	int retries = MLX5_VDPA_INTR_RETRIES;
+	int ret = -EAGAIN;
 
+	if (virtq->intr_handle.fd) {
+		while (retries-- && ret == -EAGAIN) {
+			ret = rte_intr_callback_unregister(&virtq->intr_handle,
+							mlx5_vdpa_virtq_handler,
+							virtq);
+			if (ret == -EAGAIN) {
+				DRV_LOG(DEBUG, "Try again to unregister fd %d "
+					"of virtq %d interrupt, retries = %d.",
+					virtq->intr_handle.fd,
+					(int)virtq->index, retries);
+				usleep(MLX5_VDPA_INTR_RETRIES_USEC);
+			}
+		}
+		memset(&virtq->intr_handle, 0, sizeof(virtq->intr_handle));
+	}
 	if (virtq->virtq) {
 		claim_zero(mlx5_devx_cmd_destroy(virtq->virtq));
 		virtq->virtq = NULL;
@@ -57,6 +101,14 @@ mlx5_vdpa_virtqs_release(struct mlx5_vdpa_priv *priv)
 		claim_zero(mlx5_devx_cmd_destroy(priv->td));
 		priv->td = NULL;
 	}
+	if (priv->virtq_db_addr) {
+		claim_zero(munmap(priv->virtq_db_addr, priv->var->length));
+		priv->virtq_db_addr = NULL;
+	}
+	if (priv->var) {
+		mlx5_glue->dv_free_var(priv->var);
+		priv->var = NULL;
+	}
 	priv->features = 0;
 }
 
@@ -201,6 +253,17 @@ mlx5_vdpa_virtq_setup(struct mlx5_vdpa_priv *priv,
 	if (mlx5_vdpa_virtq_modify(virtq, 1))
 		goto error;
 	virtq->enable = 1;
+	virtq->intr_handle.fd = vq.kickfd;
+	virtq->intr_handle.type = RTE_INTR_HANDLE_EXT;
+	if (rte_intr_callback_register(&virtq->intr_handle,
+				       mlx5_vdpa_virtq_handler, virtq)) {
+		virtq->intr_handle.fd = 0;
+		DRV_LOG(ERR, "Failed to register virtq %d interrupt.", index);
+		goto error;
+	} else {
+		DRV_LOG(DEBUG, "Register fd %d interrupt for virtq %d.",
+			virtq->intr_handle.fd, index);
+	}
 	return 0;
 error:
 	mlx5_vdpa_virtq_unset(virtq);
@@ -275,6 +338,23 @@ mlx5_vdpa_virtqs_prepare(struct mlx5_vdpa_priv *priv)
 		DRV_LOG(ERR, "Failed to configure negotiated features.");
 		return -1;
 	}
+	priv->var = mlx5_glue->dv_alloc_var(priv->ctx, 0);
+	if (!priv->var) {
+		DRV_LOG(ERR, "Failed to allocate VAR %u.\n", errno);
+		return -1;
+	}
+	/* Always map the entire page. */
+	priv->virtq_db_addr = mmap(NULL, priv->var->length, PROT_READ |
+				   PROT_WRITE, MAP_SHARED, priv->ctx->cmd_fd,
+				   priv->var->mmap_off);
+	if (priv->virtq_db_addr == MAP_FAILED) {
+		DRV_LOG(ERR, "Failed to map doorbell page %u.", errno);
+		priv->virtq_db_addr = NULL;
+		goto error;
+	} else {
+		DRV_LOG(DEBUG, "VAR address of doorbell mapping is %p.",
+			priv->virtq_db_addr);
+	}
 	priv->td = mlx5_devx_cmd_create_td(priv->ctx);
 	if (!priv->td) {
 		DRV_LOG(ERR, "Failed to create transport domain.");