[virtio-dev] Re: [RFC PATCH v3 3/3] SPI: Add virtio SPI driver.

On 2/13/2024 9:53 PM, Harald Mommer wrote:
> From: Harald Mommer <[email protected]>
> 
> This is the virtio SPI Linux kernel driver.
> 
> Signed-off-by: Harald Mommer <[email protected]>
> ---
>   drivers/spi/Kconfig      |  11 +
>   drivers/spi/Makefile     |   1 +
>   drivers/spi/spi-virtio.c | 475 +++++++++++++++++++++++++++++++++++++++
>   3 files changed, 487 insertions(+)
>   create mode 100644 drivers/spi/spi-virtio.c
> 
> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> index bc7021da2fe9..0b5cd4c1f06b 100644
> --- a/drivers/spi/Kconfig
> +++ b/drivers/spi/Kconfig
> @@ -1125,6 +1125,17 @@ config SPI_UNIPHIER
>   
>   	  If your SoC supports SCSSI, say Y here.
>   
> +config SPI_VIRTIO
> +	tristate "Virtio SPI Controller"
> +	depends on SPI_MASTER && VIRTIO
> +	help
> +	  This enables the Virtio SPI driver.
> +
> +	  Virtio SPI is an SPI driver for virtual machines using Virtio.
> +
> +	  If your Linux is a virtual machine using Virtio, say Y here.
> +	  If unsure, say N.
> +
>   config SPI_XCOMM
>   	tristate "Analog Devices AD-FMCOMMS1-EBZ SPI-I2C-bridge driver"
>   	depends on I2C
> diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
> index 4ff8d725ba5e..ff2243e44e00 100644
> --- a/drivers/spi/Makefile
> +++ b/drivers/spi/Makefile
> @@ -146,6 +146,7 @@ spi-thunderx-objs			:= spi-cavium.o spi-cavium-thunderx.o
>   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
> diff --git a/drivers/spi/spi-virtio.c b/drivers/spi/spi-virtio.c
> new file mode 100644
> index 000000000000..700cb36e815f
> --- /dev/null
> +++ b/drivers/spi/spi-virtio.c
> @@ -0,0 +1,475 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * SPI bus driver for the Virtio SPI controller
> + * Copyright (C) 2023 OpenSynergy GmbH
> + */
> +
> +#include <linux/completion.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/spi/spi.h>
> +#include <linux/stddef.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_ring.h>
> +#include <linux/virtio_spi.h>
> +
> +/* virtio_spi private data structure */
> +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;
> +};
> +
> +struct virtio_spi_req {
> +	struct completion completion;
> +	struct spi_transfer_head transfer_head	____cacheline_aligned;
> +	const uint8_t *tx_buf			____cacheline_aligned;
> +	uint8_t *rx_buf				____cacheline_aligned;
> +	struct spi_transfer_result result	____cacheline_aligned;
> +};
> +

Hello Harald,

     Do you add the "spi-virtio" in spidev_spi_ids in spidev.c when you 
doing the tests? And any other method to expose the spidev interface to 
userspace?

> +static struct spi_board_info board_info = {
> +	.modalias = "spi-virtio",
> +};
> +
> +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);
> +}
> +
> +/*
> + * See also
> + * https://lore.kernel.org/all/[email protected]
> + */

     For setting delay function, looks good to me. And I will look into 
other parts.

Thanks
> +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((u32)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;
> +	}
> +	if (cs_word_delay_spi > cs_word_delay_xfer)
> +		th->word_delay_ns = cpu_to_le32((u32)cs_word_delay_spi);
> +	else
> +		th->word_delay_ns = cpu_to_le32((u32)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((u32)delay + (u32)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((u32)cs_inactive +
> +						      (u32)cs_change_delay);
> +
> +	return 0;
> +}
> +
> +static int virtio_spi_one_transfer(struct virtio_spi_req *spi_req,
> +				   struct spi_controller *ctrl,
> +				   struct spi_message *msg,
> +				   struct spi_transfer *xfer)
> +{
> +	struct virtio_spi_priv *priv = spi_controller_get_devdata(ctrl);
> +	struct spi_device *spi = msg->spi;
> +	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 = 0u;
> +	unsigned int incnt = 0u;
> +	int ret;
> +
> +	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;
> +	/*
> +	 * Got comment: "The virtio spec for cs_change is *not* what the Linux
> +	 * cs_change field does, this will not do the right thing."
> +	 * TODO: Understand/discuss this, still unclear what may be wrong here
> +	 */
> +	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;
> +
> +	BUILD_BUG_ON(VIRTIO_SPI_CPHA != SPI_CPHA);
> +	BUILD_BUG_ON(VIRTIO_SPI_CPOL != SPI_CPOL);
> +	BUILD_BUG_ON(VIRTIO_SPI_CS_HIGH != SPI_CS_HIGH);
> +	BUILD_BUG_ON(VIRTIO_SPI_MODE_LSB_FIRST != SPI_LSB_FIRST);
> +
> +	th->mode = cpu_to_le32(spi->mode & (SPI_LSB_FIRST | SPI_CS_HIGH |
> +					    SPI_CPOL | SPI_CPHA));
> +	if ((spi->mode & SPI_LOOP) != 0)
> +		th->mode |= cpu_to_le32(VIRTIO_SPI_MODE_LOOP);
> +
> +	th->freq = cpu_to_le32(xfer->speed_hz);
> +
> +	if (virtio_spi_set_delays(th, spi, xfer))
> +		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 + incnt] = &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);
> +
> +msg_done:
> +	if (ret)
> +		msg->status = ret;
> +
> +	return ret;
> +}
> +
> +static int virtio_spi_transfer_one_message(struct spi_controller *ctrl,
> +					   struct spi_message *msg)
> +{
> +	struct virtio_spi_priv *priv = spi_controller_get_devdata(ctrl);
> +	struct virtio_spi_req *spi_req;
> +	struct spi_transfer *xfer;
> +	int ret = 0;
> +
> +	spi_req = kzalloc(sizeof(*spi_req), GFP_KERNEL);
> +	if (!spi_req) {
> +		ret = -ENOMEM;
> +		goto no_mem;
> +	}
> +
> +	/*
> +	 * Simple implementation: Process message by message and wait for each
> +	 * message to be completed by the device side.
> +	 */
> +	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> +		ret = virtio_spi_one_transfer(spi_req, ctrl, msg, xfer);
> +		if (ret)
> +			goto msg_done;
> +
> +		virtqueue_kick(priv->vq);
> +
> +		wait_for_completion(&spi_req->completion);
> +
> +		/* Read result from message */
> +		ret = (int)spi_req->result.result;
> +		if (ret)
> +			goto msg_done;
> +	}
> +
> +msg_done:
> +	kfree(spi_req);
> +no_mem:
> +	msg->status = ret;
> +	spi_finalize_current_message(ctrl);
> +
> +	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) != 0)
> +		ctrl->mode_bits |= VIRTIO_SPI_CPHA;
> +	if ((priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_CPOL_1) != 0)
> +		ctrl->mode_bits |= VIRTIO_SPI_CPOL;
> +	if ((priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_LSB_FIRST) != 0)
> +		ctrl->mode_bits |= SPI_LSB_FIRST;
> +	if ((priv->mode_func_supported & VIRTIO_SPI_MF_SUPPORT_LOOPBACK) != 0)
> +		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) != 0)
> +		ctrl->mode_bits |= SPI_TX_DUAL;
> +	if ((tx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_QUAD) != 0)
> +		ctrl->mode_bits |= SPI_TX_QUAD;
> +	if ((tx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_OCTAL) != 0)
> +		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) != 0)
> +		ctrl->mode_bits |= SPI_RX_DUAL;
> +	if ((rx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_QUAD) != 0)
> +		ctrl->mode_bits |= SPI_RX_QUAD;
> +	if ((rx_nbits_supported & VIRTIO_SPI_RX_TX_SUPPORT_OCTAL) != 0)
> +		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 (int)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(struct virtio_device *vdev)
> +{
> +	virtio_reset_device(vdev);
> +	vdev->config->del_vqs(vdev);
> +}
> +
> +static int virtio_spi_validate(struct virtio_device *vdev)
> +{
> +	/*
> +	 * SPI needs always access to the config space.
> +	 * Check that the driver can access the config space
> +	 */
> +	if (!vdev->config->get) {
> +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> +			__func__);
> +		return -EINVAL;
> +	}
> +
> +	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> +		dev_err(&vdev->dev,
> +			"device does not comply with spec version 1.x\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtio_spi_probe(struct virtio_device *vdev)
> +{
> +	struct device_node *np = vdev->dev.parent->of_node;
> +	struct virtio_spi_priv *priv;
> +	struct spi_controller *ctrl;
> +	int err;
> +	u32 bus_num;
> +	u16 csi;
> +
> +	ctrl = devm_spi_alloc_host(&vdev->dev, sizeof(*priv));
> +	if (!ctrl) {
> +		dev_err(&vdev->dev, "Kernel memory exhausted in %s()\n",
> +			__func__);
> +		return -ENOMEM;
> +	}
> +
> +	priv = spi_controller_get_devdata(ctrl);
> +	priv->vdev = vdev;
> +	vdev->priv = priv;
> +	dev_set_drvdata(&vdev->dev, ctrl);
> +
> +	err = of_property_read_u32(np, "spi,bus-num", &bus_num);
> +	if (!err && bus_num <= S16_MAX)
> +		ctrl->bus_num = (s16)bus_num;
> +
> +	virtio_spi_read_config(vdev);
> +
> +	/* Method to transfer a single SPI message */
> +	ctrl->transfer_one_message = virtio_spi_transfer_one_message;
> +
> +	/* Initialize virtqueues */
> +	err = virtio_spi_find_vqs(priv);
> +	if (err) {
> +		dev_err(&vdev->dev, "Cannot setup virtqueues\n");
> +		return err;
> +	}
> +
> +	err = spi_register_controller(ctrl);
> +	if (err) {
> +		dev_err(&vdev->dev, "Cannot register controller\n");
> +		goto err_return;
> +	}
> +
> +	board_info.max_speed_hz = priv->max_freq_hz;
> +	/* spi_new_device() currently does not use bus_num but better set it */
> +	board_info.bus_num = (u16)ctrl->bus_num;
> +
> +	/* Add chip selects to controller */
> +	for (csi = 0; csi < ctrl->num_chipselect; csi++) {
> +		dev_dbg(&vdev->dev, "Setting up CS=%u\n", csi);
> +		board_info.chip_select = csi;
> +		/* TODO: Discuss setting of board_info.mode */
> +		if (!(priv->mode_func_supported & VIRTIO_SPI_CS_HIGH))
> +			board_info.mode = SPI_MODE_0;
> +		else
> +			board_info.mode = SPI_MODE_0 | SPI_CS_HIGH;
> +		if (!spi_new_device(ctrl, &board_info)) {
> +			dev_err(&vdev->dev, "Cannot setup device %u\n", csi);
> +			spi_unregister_controller(ctrl);
> +			err = -ENODEV;
> +			goto err_return;
> +		}
> +	}
> +
> +	return 0;
> +
> +err_return:
> +	vdev->config->del_vqs(vdev);
> +	return err;
> +}
> +
> +static void virtio_spi_remove(struct virtio_device *vdev)
> +{
> +	struct spi_controller *ctrl = dev_get_drvdata(&vdev->dev);
> +
> +	/* Order: 1.) unregister controller, 2.) remove virtqueue */
> +	spi_unregister_controller(ctrl);
> +	virtio_spi_del_vq(vdev);
> +}
> +
> +static int virtio_spi_freeze(struct virtio_device *vdev)
> +{
> +	struct device *dev = &vdev->dev;
> +	struct spi_controller *ctrl = dev_get_drvdata(dev);
> +	int ret;
> +
> +	/* Stop the queue running */
> +	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 virtio_device *vdev)
> +{
> +	struct device *dev = &vdev->dev;
> +	struct spi_controller *ctrl = dev_get_drvdata(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 },
> +	{ 0 },
> +};
> +
> +static struct virtio_driver virtio_spi_driver = {
> +	.driver.name = KBUILD_MODNAME,
> +	.driver.owner = THIS_MODULE,
> +	.id_table = virtio_spi_id_table,
> +	.validate = virtio_spi_validate,
> +	.probe = virtio_spi_probe,
> +	.remove = virtio_spi_remove,
> +	.freeze = pm_sleep_ptr(virtio_spi_freeze),
> +	.restore = pm_sleep_ptr(virtio_spi_restore),
> +};
> +
> +module_virtio_driver(virtio_spi_driver);
> +MODULE_DEVICE_TABLE(virtio, virtio_spi_id_table);
> +
> +MODULE_AUTHOR("OpenSynergy GmbH");
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Virtio SPI bus driver");

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