SPI: Add virtio SPI driver

This is the virtio SPI Linux kernel driver.

Signed-off-by: Haixu Cui <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

MAINTAINERS

···
 M:	Haixu Cui <[e-mail]>
 L:	[e-mail]
 S:	Maintained
+F:	drivers/spi/spi-virtio.c
 F:	include/uapi/linux/virtio_spi.h
 
 VIRTUAL BOX GUEST DEVICE DRIVER

drivers/spi/Kconfig

···
 
 	  If your SoC supports SCSSI, say Y here.
 
+config SPI_VIRTIO
+	tristate "Virtio SPI Controller"
+	depends on SPI_MASTER && VIRTIO
+	help
+	  If you say yes to this option, support will be included for the virtio
+	  SPI controller driver. The hardware can be emulated by any device model
+	  software according to the virtio protocol.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called spi-virtio.
+
 config SPI_XCOMM
 	tristate "Analog Devices AD-FMCOMMS1-EBZ SPI-I2C-bridge driver"
 	depends on I2C

drivers/spi/Makefile

···
 obj-$(CONFIG_SPI_THUNDERX)		+= spi-thunderx.o
 obj-$(CONFIG_SPI_TOPCLIFF_PCH)		+= spi-topcliff-pch.o
 obj-$(CONFIG_SPI_UNIPHIER)		+= spi-uniphier.o
+obj-$(CONFIG_SPI_VIRTIO)		+= spi-virtio.o
 obj-$(CONFIG_SPI_XCOMM)		+= spi-xcomm.o
 obj-$(CONFIG_SPI_XILINX)		+= spi-xilinx.o
 obj-$(CONFIG_SPI_XLP)			+= spi-xlp.o

drivers/spi/spi-virtio.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * SPI bus driver for the Virtio SPI controller
+ * Copyright (C) 2023 OpenSynergy GmbH
+ * Copyright (C) 2025 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/completion.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/stddef.h>
+#include <linux/virtio.h>
+#include <linux/virtio_ring.h>
+#include <linux/virtio_spi.h>
+
+#define VIRTIO_SPI_MODE_MASK \
+	(SPI_MODE_X_MASK | SPI_CS_HIGH | SPI_LSB_FIRST)
+
+struct virtio_spi_req {
+	struct completion completion;
+	const u8 *tx_buf;
+	u8 *rx_buf;
+	struct spi_transfer_head transfer_head	____cacheline_aligned;
+	struct spi_transfer_result result;
+};
+
+struct virtio_spi_priv {
+	/* The virtio device we're associated with */
+	struct virtio_device *vdev;
+	/* Pointer to the virtqueue */
+	struct virtqueue *vq;
+	/* Copy of config space mode_func_supported */
+	u32 mode_func_supported;
+	/* Copy of config space max_freq_hz */
+	u32 max_freq_hz;
+};
+
+static void virtio_spi_msg_done(struct virtqueue *vq)
+{
+	struct virtio_spi_req *req;
+	unsigned int len;
+
+	while ((req = virtqueue_get_buf(vq, &len)))
+		complete(&req->completion);
+}
+
+/*
+ * virtio_spi_set_delays - Set delay parameters for SPI transfer
+ *
+ * This function sets various delay parameters for SPI transfer,
+ * including delay after CS asserted, timing intervals between
+ * adjacent words within a transfer, delay before and after CS
+ * deasserted. It converts these delay parameters to nanoseconds
+ * using spi_delay_to_ns and stores the results in spi_transfer_head
+ * structure.
+ * If the conversion fails, the function logs a warning message and
+ * returns an error code.
+ *       .   .      .    .    .   .   .   .   .   .
+ * Delay + A +      + B  +    + C + D + E + F + A +
+ *       .   .      .    .    .   .   .   .   .   .
+ *    ___.   .      .    .    .   .   .___.___.   .
+ * CS#   |___.______.____.____.___.___|   .   |___._____________
+ *       .   .      .    .    .   .   .   .   .   .
+ *       .   .      .    .    .   .   .   .   .   .
+ * SCLK__.___.___NNN_____NNN__.___.___.___.___.___.___NNN_______
+ *
+ * NOTE: 1st transfer has two words, the delay between these two words are
+ * 'B' in the diagram.
+ *
+ * A => struct spi_device -> cs_setup
+ * B => max{struct spi_transfer -> word_delay, struct spi_device -> word_delay}
+ *   Note: spi_device and spi_transfer both have word_delay, Linux
+ *         choose the bigger one, refer to _spi_xfer_word_delay_update function
+ * C => struct spi_transfer -> delay
+ * D => struct spi_device -> cs_hold
+ * E => struct spi_device -> cs_inactive
+ * F => struct spi_transfer -> cs_change_delay
+ *
+ * So the corresponding relationship:
+ * A   <===> cs_setup_ns (after CS asserted)
+ * B   <===> word_delay_ns (delay between adjacent words within a transfer)
+ * C+D <===> cs_delay_hold_ns (before CS deasserted)
+ * E+F <===> cs_change_delay_inactive_ns (after CS deasserted, these two
+ * values are also recommended in the Linux driver to be added up)
+ */
+static int virtio_spi_set_delays(struct spi_transfer_head *th,
+				 struct spi_device *spi,
+				 struct spi_transfer *xfer)
+{
+	int cs_setup;
+	int cs_word_delay_xfer;
+	int cs_word_delay_spi;
+	int delay;
+	int cs_hold;
+	int cs_inactive;
+	int cs_change_delay;
+
+	cs_setup = spi_delay_to_ns(&spi->cs_setup, xfer);
+	if (cs_setup < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_setup\n");
+		return cs_setup;
+	}
+	th->cs_setup_ns = cpu_to_le32(cs_setup);
+
+	cs_word_delay_xfer = spi_delay_to_ns(&xfer->word_delay, xfer);
+	if (cs_word_delay_xfer < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_word_delay_xfer\n");
+		return cs_word_delay_xfer;
+	}
+	cs_word_delay_spi = spi_delay_to_ns(&spi->word_delay, xfer);
+	if (cs_word_delay_spi < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_word_delay_spi\n");
+		return cs_word_delay_spi;
+	}
+
+	th->word_delay_ns = cpu_to_le32(max(cs_word_delay_spi, cs_word_delay_xfer));
+
+	delay = spi_delay_to_ns(&xfer->delay, xfer);
+	if (delay < 0) {
+		dev_warn(&spi->dev, "Cannot convert delay\n");
+		return delay;
+	}
+	cs_hold = spi_delay_to_ns(&spi->cs_hold, xfer);
+	if (cs_hold < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_hold\n");
+		return cs_hold;
+	}
+	th->cs_delay_hold_ns = cpu_to_le32(delay + cs_hold);
+
+	cs_inactive = spi_delay_to_ns(&spi->cs_inactive, xfer);
+	if (cs_inactive < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_inactive\n");
+		return cs_inactive;
+	}
+	cs_change_delay = spi_delay_to_ns(&xfer->cs_change_delay, xfer);
+	if (cs_change_delay < 0) {
+		dev_warn(&spi->dev, "Cannot convert cs_change_delay\n");
+		return cs_change_delay;
+	}
+	th->cs_change_delay_inactive_ns =
+		cpu_to_le32(cs_inactive + cs_change_delay);
+
+	return 0;
+}
+
+static int virtio_spi_transfer_one(struct spi_controller *ctrl,
+				   struct spi_device *spi,
+				   struct spi_transfer *xfer)
+{
+	struct virtio_spi_priv *priv = spi_controller_get_devdata(ctrl);
+	struct virtio_spi_req *spi_req __free(kfree) = NULL;
+	struct spi_transfer_head *th;
+	struct scatterlist sg_out_head, sg_out_payload;
+	struct scatterlist sg_in_result, sg_in_payload;
+	struct scatterlist *sgs[4];
+	unsigned int outcnt = 0;
+	unsigned int incnt = 0;
+	int ret;
+
+	spi_req = kzalloc(sizeof(*spi_req), GFP_KERNEL);
+	if (!spi_req)
+		return -ENOMEM;
+
+	init_completion(&spi_req->completion);
+
+	th = &spi_req->transfer_head;
+
+	/* Fill struct spi_transfer_head */
+	th->chip_select_id = spi_get_chipselect(spi, 0);
+	th->bits_per_word = spi->bits_per_word;
+	th->cs_change = xfer->cs_change;
+	th->tx_nbits = xfer->tx_nbits;
+	th->rx_nbits = xfer->rx_nbits;
+	th->reserved[0] = 0;
+	th->reserved[1] = 0;
+	th->reserved[2] = 0;
+
+	static_assert(VIRTIO_SPI_CPHA == SPI_CPHA,
+		      "VIRTIO_SPI_CPHA must match SPI_CPHA");
+	static_assert(VIRTIO_SPI_CPOL == SPI_CPOL,
+		      "VIRTIO_SPI_CPOL must match SPI_CPOL");
+	static_assert(VIRTIO_SPI_CS_HIGH == SPI_CS_HIGH,
+		      "VIRTIO_SPI_CS_HIGH must match SPI_CS_HIGH");
+	static_assert(VIRTIO_SPI_MODE_LSB_FIRST == SPI_LSB_FIRST,
+		      "VIRTIO_SPI_MODE_LSB_FIRST must match SPI_LSB_FIRST");
+
+	th->mode = cpu_to_le32(spi->mode & VIRTIO_SPI_MODE_MASK);
+	if (spi->mode & SPI_LOOP)
+		th->mode |= cpu_to_le32(VIRTIO_SPI_MODE_LOOP);
+
+	th->freq = cpu_to_le32(xfer->speed_hz);
+
+	ret = virtio_spi_set_delays(th, spi, xfer);
+	if (ret)
+		goto msg_done;
+
+	/* Set buffers */
+	spi_req->tx_buf = xfer->tx_buf;
+	spi_req->rx_buf = xfer->rx_buf;
+
+	/* Prepare sending of virtio message */
+	init_completion(&spi_req->completion);
+
+	sg_init_one(&sg_out_head, th, sizeof(*th));
+	sgs[outcnt] = &sg_out_head;
+	outcnt++;
+
+	if (spi_req->tx_buf) {
+		sg_init_one(&sg_out_payload, spi_req->tx_buf, xfer->len);
+		sgs[outcnt] = &sg_out_payload;
+		outcnt++;
+	}
+
+	if (spi_req->rx_buf) {
+		sg_init_one(&sg_in_payload, spi_req->rx_buf, xfer->len);
+		sgs[outcnt] = &sg_in_payload;
+		incnt++;
+	}
+
+	sg_init_one(&sg_in_result, &spi_req->result,
+		    sizeof(struct spi_transfer_result));
+	sgs[outcnt + incnt] = &sg_in_result;
+	incnt++;
+
+	ret = virtqueue_add_sgs(priv->vq, sgs, outcnt, incnt, spi_req,
+				GFP_KERNEL);
+	if (ret)
+		goto msg_done;
+
+	/* Simple implementation: There can be only one transfer in flight */
+	virtqueue_kick(priv->vq);
+
+	wait_for_completion(&spi_req->completion);
+
+	/* Read result from message and translate return code */
+	switch (spi_req->result.result) {
+	case VIRTIO_SPI_TRANS_OK:
+		break;
+	case VIRTIO_SPI_PARAM_ERR:
+		ret = -EINVAL;
+		break;
+	case VIRTIO_SPI_TRANS_ERR:
+		ret = -EIO;
+		break;
+	default:
+		ret = -EIO;
+		break;
+	}
+
+msg_done:
+	if (ret)
+		ctrl->cur_msg->status = ret;
+
+	return ret;
+}
+
+static void virtio_spi_read_config(struct virtio_device *vdev)
+{
+	struct spi_controller *ctrl = dev_get_drvdata(&vdev->dev);
+	struct virtio_spi_priv *priv = vdev->priv;
+	u8 cs_max_number;
+	u8 tx_nbits_supported;
+	u8 rx_nbits_supported;
+
+	cs_max_number = virtio_cread8(vdev, offsetof(struct virtio_spi_config,
+						     cs_max_number));
+	ctrl->num_chipselect = cs_max_number;
+
+	/* Set the mode bits which are understood by this driver */
+	priv->mode_func_supported =
+		virtio_cread32(vdev, offsetof(struct virtio_spi_config,
+					      mode_func_supported));
+	ctrl->mode_bits = priv->mode_func_supported &
+			  (VIRTIO_SPI_CS_HIGH | VIRTIO_SPI_MODE_LSB_FIRST);
+	if (priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_CPHA_1)
+		ctrl->mode_bits |= VIRTIO_SPI_CPHA;
+	if (priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_CPOL_1)
+		ctrl->mode_bits |= VIRTIO_SPI_CPOL;
+	if (priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_LSB_FIRST)
+		ctrl->mode_bits |= SPI_LSB_FIRST;
+	if (priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_LOOPBACK)
+		ctrl->mode_bits |= SPI_LOOP;
+	tx_nbits_supported =
+		virtio_cread8(vdev, offsetof(struct virtio_spi_config,
+					     tx_nbits_supported));
+	if (tx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_DUAL)
+		ctrl->mode_bits |= SPI_TX_DUAL;
+	if (tx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_QUAD)
+		ctrl->mode_bits |= SPI_TX_QUAD;
+	if (tx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_OCTAL)
+		ctrl->mode_bits |= SPI_TX_OCTAL;
+	rx_nbits_supported =
+		virtio_cread8(vdev, offsetof(struct virtio_spi_config,
+					     rx_nbits_supported));
+	if (rx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_DUAL)
+		ctrl->mode_bits |= SPI_RX_DUAL;
+	if (rx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_QUAD)
+		ctrl->mode_bits |= SPI_RX_QUAD;
+	if (rx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_OCTAL)
+		ctrl->mode_bits |= SPI_RX_OCTAL;
+
+	ctrl->bits_per_word_mask =
+		virtio_cread32(vdev, offsetof(struct virtio_spi_config,
+					      bits_per_word_mask));
+
+	priv->max_freq_hz =
+		virtio_cread32(vdev, offsetof(struct virtio_spi_config,
+					      max_freq_hz));
+}
+
+static int virtio_spi_find_vqs(struct virtio_spi_priv *priv)
+{
+	struct virtqueue *vq;
+
+	vq = virtio_find_single_vq(priv->vdev, virtio_spi_msg_done, "spi-rq");
+	if (IS_ERR(vq))
+		return PTR_ERR(vq);
+	priv->vq = vq;
+	return 0;
+}
+
+/* Function must not be called before virtio_spi_find_vqs() has been run */
+static void virtio_spi_del_vq(void *data)
+{
+	struct virtio_device *vdev = data;
+
+	virtio_reset_device(vdev);
+	vdev->config->del_vqs(vdev);
+}
+
+static int virtio_spi_probe(struct virtio_device *vdev)
+{
+	struct virtio_spi_priv *priv;
+	struct spi_controller *ctrl;
+	int ret;
+
+	ctrl = devm_spi_alloc_host(&vdev->dev, sizeof(*priv));
+	if (!ctrl)
+		return -ENOMEM;
+
+	priv = spi_controller_get_devdata(ctrl);
+	priv->vdev = vdev;
+	vdev->priv = priv;
+
+	device_set_node(&ctrl->dev, dev_fwnode(&vdev->dev));
+
+	dev_set_drvdata(&vdev->dev, ctrl);
+
+	virtio_spi_read_config(vdev);
+
+	ctrl->transfer_one = virtio_spi_transfer_one;
+
+	ret = virtio_spi_find_vqs(priv);
+	if (ret)
+		return dev_err_probe(&vdev->dev, ret, "Cannot setup virtqueues\n");
+
+	/* Register cleanup for virtqueues using devm */
+	ret = devm_add_action_or_reset(&vdev->dev, virtio_spi_del_vq, vdev);
+	if (ret)
+		return dev_err_probe(&vdev->dev, ret, "Cannot register virtqueue cleanup\n");
+
+	/* Use devm version to register controller */
+	ret = devm_spi_register_controller(&vdev->dev, ctrl);
+	if (ret)
+		return dev_err_probe(&vdev->dev, ret, "Cannot register controller\n");
+
+	return 0;
+}
+
+static int virtio_spi_freeze(struct device *dev)
+{
+	struct spi_controller *ctrl = dev_get_drvdata(dev);
+	struct virtio_device *vdev = dev_to_virtio(dev);
+	int ret;
+
+	ret = spi_controller_suspend(ctrl);
+	if (ret) {
+		dev_warn(dev, "cannot suspend controller (%d)\n", ret);
+		return ret;
+	}
+
+	virtio_spi_del_vq(vdev);
+	return 0;
+}
+
+static int virtio_spi_restore(struct device *dev)
+{
+	struct spi_controller *ctrl = dev_get_drvdata(dev);
+	struct virtio_device *vdev = dev_to_virtio(dev);
+	int ret;
+
+	ret = virtio_spi_find_vqs(vdev->priv);
+	if (ret) {
+		dev_err(dev, "problem starting vqueue (%d)\n", ret);
+		return ret;
+	}
+
+	ret = spi_controller_resume(ctrl);
+	if (ret)
+		dev_err(dev, "problem resuming controller (%d)\n", ret);
+
+	return ret;
+}
+
+static struct virtio_device_id virtio_spi_id_table[] = {
+	{ VIRTIO_ID_SPI, VIRTIO_DEV_ANY_ID },
+	{}
+};
+MODULE_DEVICE_TABLE(virtio, virtio_spi_id_table);
+
+static const struct dev_pm_ops virtio_spi_pm_ops = {
+	.freeze = pm_sleep_ptr(virtio_spi_freeze),
+	.restore = pm_sleep_ptr(virtio_spi_restore),
+};
+
+static struct virtio_driver virtio_spi_driver = {
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.pm = &virtio_spi_pm_ops,
+	},
+	.id_table = virtio_spi_id_table,
+	.probe = virtio_spi_probe,
+};
+module_virtio_driver(virtio_spi_driver);
+
+MODULE_AUTHOR("OpenSynergy GmbH");
+MODULE_AUTHOR("Haixu Cui <[e-mail]>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Virtio SPI bus driver");