Re: [RFC PATCH v1 3/3] SPI: Add virtio SPI driver (V4 draft specification).
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Hi Harald,
Please refer to my comments below.
On 10/28/2023 12:10 AM, Harald Mommer wrote:
From: Harald Mommer <harald.mommer@xxxxxxxxxxxxxxx>
This is the first public version of the virtio SPI Linux kernel driver
compliant to the "PATCH v4" draft virtio SPI specification.
Signed-off-by: Harald Mommer <Harald.Mommer@xxxxxxxxxxxxxxx>
---
drivers/spi/Kconfig | 10 +
drivers/spi/Makefile | 1 +
drivers/spi/spi-virtio.c | 513 +++++++++++++++++++++++++++++++++++++++
3 files changed, 524 insertions(+)
create mode 100644 drivers/spi/spi-virtio.c
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 35dbfacecf1c..55f45c5a8d82 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -1125,6 +1125,16 @@ config SPI_UNIPHIER
If your SoC supports SCSSI, say Y here.
+config SPI_VIRTIO
+ tristate "Virtio SPI SPI Controller"
+ depends on 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.
+
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..12a4d96555f1
--- /dev/null
+++ b/drivers/spi/spi-virtio.c
@@ -0,0 +1,513 @@
+// 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/stddef.h>
+#include <linux/virtio.h>
+#include <linux/virtio_ring.h>
+#include <linux/version.h>
+#include <linux/spi/spi.h>
+#include <linux/virtio_spi.h>
+
+/* SPI device queues */
+#define VIRTIO_SPI_QUEUE_RQ 0
+#define VIRTIO_SPI_QUEUE_COUNT 1
+
+/* virtio_spi private data structure */
+struct virtio_spi_priv {
+ /* The virtio device we're associated with */
+ struct virtio_device *vdev;
+ /* The virtqueues */
+ struct virtqueue *vqs[VIRTIO_SPI_QUEUE_COUNT];
+ /* I/O callback function pointers for the virtqueues */
+ vq_callback_t *io_callbacks[VIRTIO_SPI_QUEUE_COUNT];
+ /* Support certain delay timing settings */
+ bool support_delays;
+};
+
+/* Compare with file i2c_virtio.c structure virtio_i2c_req */
+struct virtio_spi_req {
+ struct completion completion;
+#ifdef DEBUG
+ unsigned int rx_len;
+#endif
+ // clang-format off
+ 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;
+ // clang-format on
+};
+
+static struct spi_board_info board_info = {
+ .modalias = "spi-virtio",
+ .max_speed_hz = 125000000, /* Arbitrary very high limit */
+ .bus_num = 0, /* Patched later during initialization */
+ .chip_select = 0, /* Patched later during initialization */
+ .mode = SPI_MODE_0,
+};
+
+/* Compare with file i2c_virtio.c structure virtio_i2c_msg_done */
+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);
+}
+
+static int virtio_spi_one_transfer(struct virtio_spi_req *spi_req,
+ struct spi_master *master,
+ struct spi_message *msg,
+ struct spi_transfer *xfer)
+{
+ struct virtio_spi_priv *priv = spi_master_get_devdata(master);
+ struct device *dev = &priv->vdev->dev;
+ struct virtqueue *vq = priv->vqs[VIRTIO_SPI_QUEUE_RQ];
+ 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->slave_id = spi->chip_select;
+ 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;
+
+#if (VIRTIO_SPI_CPHA != SPI_CPHA)
+#error VIRTIO_SPI_CPHA != SPI_CPHA
+#endif
+
+#if (VIRTIO_SPI_CPOL != SPI_CPOL)
+#error VIRTIO_SPI_CPOL != SPI_CPOL
+#endif
+
+#if (VIRTIO_SPI_CS_HIGH != SPI_CS_HIGH)
+#error VIRTIO_SPI_CS_HIGH != SPI_CS_HIGH
+#endif
+
+#if (VIRTIO_SPI_MODE_LSB_FIRST != SPI_LSB_FIRST)
+#error VIRTIO_SPI_MODE_LSB_FIRST != SPI_LSB_FIRST
+#endif
+
+ th->mode = spi->mode &
+ (SPI_LSB_FIRST | SPI_CS_HIGH | SPI_CPOL | SPI_CPHA);
+ if ((spi->mode & SPI_LOOP) != 0)
+ th->mode |= VIRTIO_SPI_MODE_LOOP;
+
+ th->freq = cpu_to_le32(xfer->speed_hz);
+
+ ret = spi_delay_to_ns(&xfer->word_delay, xfer);
+ if (ret < 0) {
+ dev_warn(dev, "Cannot convert word_delay\n");
+ goto msg_done;
+ }
+ th->word_delay_ns = cpu_to_le32((u32)ret);
+
+ ret = spi_delay_to_ns(&xfer->delay, xfer);
+ if (ret < 0) {
+ dev_warn(dev, "Cannot convert delay\n");
+ goto msg_done;
+ }
+ th->cs_setup_ns = cpu_to_le32((u32)ret);
+ th->cs_delay_hold_ns = cpu_to_le32((u32)ret);
+
+ /* This is the "off" time when CS has to be deasserted for a moment */
+ ret = spi_delay_to_ns(&xfer->cs_change_delay, xfer);
+ if (ret < 0) {
+ dev_warn(dev, "Cannot convert cs_change_delay\n");
+ goto msg_done;
+ }
+ th->cs_change_delay_inactive_ns = cpu_to_le32((u32)ret);
+
+ /*
+ * With the way it's specified in the virtio draft specification
+ * V4 the virtio device just MUST print a warning and ignores the delay
+ * timing settings it does not support.
+ * Implementation decision: Only warn once not to flood the logs.
+ * TODO: Comment on this
+ * By the wording of the speciification it is unclear which timings
+ * exactly are affected, there is a copy & paste mistake in the spec.
+ * TODO: Comment on this
+ * Somewhat unclear is whether the values in question are to be
+ * passed as is to the virtio device.
+ *
+ * Probably better specification for the device:
+ * The device shall reject a message if tbd delay timing is not
+ * supported but the requested value is not zero by some tbd error.
+ * Probably better specification for the driver:
+ * If the device did not announce support of delay timings in the
+ * config space the driver SHOULD not sent a delay timing not equal to
+ * zero but should immediately reject the message.
+ */
+ if (!priv->support_delays) {
+ if (th->word_delay_ns)
+ dev_warn_once(dev, "word_delay_ns != 0\n");
+ if (th->cs_setup_ns)
+ dev_warn_once(dev, "cs_setup_ns != 0\n");
+ if (th->cs_change_delay_inactive_ns)
+ dev_warn_once(dev,
+ "cs_change_delay_inactive_ns != 0\n");
+ }
+
+ /* Set buffers */
+ spi_req->tx_buf = xfer->tx_buf;
+ spi_req->rx_buf = xfer->rx_buf;
+#ifdef DEBUG
+ spi_req->rx_len = xfer->len;
+#endif
+
+ /* Prepare sending of virtio message */
+ init_completion(&spi_req->completion);
+
+ sg_init_one(&sg_out_head, &spi_req->transfer_head,
+ sizeof(struct spi_transfer_head));
+ sgs[outcnt] = &sg_out_head;
+
+ pr_debug("sgs[%u] len = %u", outcnt + incnt,
+ sgs[outcnt + incnt]->length);
+ pr_debug("Dump of spi_transfer_head\n");
+ print_hex_dump_debug(KBUILD_MODNAME " ", DUMP_PREFIX_NONE, 16, 1,
+ &spi_req->transfer_head,
+ sizeof(struct spi_transfer_head), true);
+ outcnt++;
+
+ if (spi_req->tx_buf) {
+ sg_init_one(&sg_out_payload, spi_req->tx_buf, xfer->len);
+ sgs[outcnt] = &sg_out_payload;
+ pr_debug("sgs[%u] len = %u", outcnt + incnt,
+ sgs[outcnt + incnt]->length);
+ pr_debug("Dump of TX payload\n");
+ print_hex_dump_debug(KBUILD_MODNAME " ", DUMP_PREFIX_NONE, 16,
+ 1, spi_req->tx_buf, xfer->len, true);
+ outcnt++;
+ }
+
+ if (spi_req->rx_buf) {
+ sg_init_one(&sg_in_payload, spi_req->rx_buf, xfer->len);
+ sgs[outcnt + incnt] = &sg_in_payload;
+ pr_debug("sgs[%u] len = %u", outcnt + incnt,
+ sgs[outcnt + incnt]->length);
+ incnt++;
+ }
+
+ sg_init_one(&sg_in_result, &spi_req->result,
+ sizeof(struct spi_transfer_result));
+ sgs[outcnt + incnt] = &sg_in_result;
+ pr_debug("sgs[%u] len = %u", outcnt + incnt,
+ sgs[outcnt + incnt]->length);
+ incnt++;
+
+ pr_debug("%s: outcnt=%u, incnt=%u\n", __func__, outcnt, incnt);
+
+ ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, spi_req, GFP_KERNEL);
+msg_done:
+ if (ret)
+ msg->status = ret;
+
+ return ret;
+}
+
This function here seems very similar with the default
transfer_one_message interface provided by Linux driver, that is
spi_transfer_one_message.
What if using the default interface? In default one, xfer->delay and
xfer->cs_change_delay are executed by software, which means these two
values don't need to pass to the backend.
+static int virtio_spi_transfer_one_message(struct spi_master *master,
+ struct spi_message *msg)
+{
+ struct virtio_spi_priv *priv = spi_master_get_devdata(master);
+ struct virtqueue *vq = priv->vqs[VIRTIO_SPI_QUEUE_RQ];
+ 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, master, msg, xfer);
+ if (ret)
+ goto msg_done;
+
+ virtqueue_kick(vq);
+
+ wait_for_completion(&spi_req->completion);
+
+ /* Read result from message */
+ ret = (int)spi_req->result.result;
+ if (ret)
+ goto msg_done;
+
+#ifdef DEBUG
+ if (spi_req->rx_buf) {
+ pr_debug("Dump of RX payload\n");
+ print_hex_dump(KERN_DEBUG, KBUILD_MODNAME " ",
+ DUMP_PREFIX_NONE, 16, 1, spi_req->rx_buf,
+ spi_req->rx_len, true);
+ }
+#endif
+ }
+
+msg_done:
+ kfree(spi_req);
+no_mem:
+ msg->status = ret;
+ /*
+ * Looking into other SPI drivers like spi-atmel.c the function
+ * spi_finalize_current_message() is supposed to be called only once
+ * for all transfers in the list and not for each single message
+ */
+ spi_finalize_current_message(master);
+ dev_dbg(&priv->vdev->dev, "%s() returning %d\n", __func__, ret);
+ return ret;
+}
+
+static void virtio_spi_read_config(struct virtio_device *vdev)
+{
+ struct spi_master *master = dev_get_drvdata(&vdev->dev);
+ struct virtio_spi_priv *priv = vdev->priv;
+ u16 bus_num;
+ u16 cs_max_number;
+ u8 support_delays;
+
+ bus_num = virtio_cread16(vdev,
+ offsetof(struct virtio_spi_config, bus_num));
+ cs_max_number = virtio_cread16(vdev, offsetof(struct virtio_spi_config,
+ chip_select_max_number));
+ support_delays =
+ virtio_cread16(vdev, offsetof(struct virtio_spi_config,
+ cs_timing_setting_enable));
+
+ if (bus_num > S16_MAX) {
+ dev_warn(&vdev->dev, "Limiting bus_num = %u to %d\n", bus_num,
+ S16_MAX);
+ bus_num = S16_MAX;
+ }
+
+ if (support_delays > 1)
+ dev_warn(&vdev->dev, "cs_timing_setting_enable = %u\n",
+ support_delays);
+ priv->support_delays = (support_delays != 0);
+ master->bus_num = (s16)bus_num;
+ master->num_chipselect = cs_max_number;
+}
+
+static int virtio_spi_find_vqs(struct virtio_spi_priv *priv)
+{
+ static const char *const io_names[VIRTIO_SPI_QUEUE_COUNT] = { "spi-rq" };
+
+ priv->io_callbacks[VIRTIO_SPI_QUEUE_RQ] = virtio_spi_msg_done;
+
+ /* Find the queues. */
+ return virtio_find_vqs(priv->vdev, VIRTIO_SPI_QUEUE_COUNT, priv->vqs,
+ priv->io_callbacks, io_names, NULL);
+}
+
+/* Compare with i2c-virtio.c function virtio_i2c_del_vqs() */
+/* Function must not be called before virtio_spi_find_vqs() has been run */
+static void virtio_spi_del_vq(struct virtio_device *vdev)
+{
+ vdev->config->reset(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 virtio_spi_priv *priv;
+ struct spi_master *master;
+ int err;
+ u16 csi;
+
+ err = -ENOMEM;
+ master = spi_alloc_master(&vdev->dev, sizeof(struct virtio_spi_priv));
+ if (!master) {
+ dev_err(&vdev->dev, "Kernel memory exhausted in %s()\n",
+ __func__);
+ goto err_return;
+ }
+
+ priv = spi_master_get_devdata(master);
+ priv->vdev = vdev;
+ vdev->priv = priv;
+ dev_set_drvdata(&vdev->dev, master);
+
+ /* the spi->mode bits understood by this driver: */
+ master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST |
+ SPI_LOOP | SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL |
+ SPI_RX_QUAD | SPI_TX_OCTAL | SPI_RX_OCTAL;
+
+ /* What most support. We don't know from the virtio device side */
+ master->bits_per_word_mask = SPI_BPW_RANGE_MASK(8, 16);
+ /* There is no associated device tree node */
+ master->dev.of_node = NULL;
+ /* Get bus_num and num_chipselect from the config space */
+ virtio_spi_read_config(vdev);
+ /* Maybe this method is not needed for virtio SPI */
+ master->setup = NULL; /* Function not needed for virtio-spi */
+ /* No restrictions to announce */
+ master->flags = 0;
+ /* Method to transfer a single SPI message */
+ master->transfer_one_message = virtio_spi_transfer_one_message;
+ /* Method to cleanup the driver */
+ master->cleanup = NULL; /* Function not needed for virtio-spi */
+
+ /* Initialize virtqueues */
+ err = virtio_spi_find_vqs(priv);
+ if (err) {
+ dev_err(&vdev->dev, "Cannot setup virtqueues\n");
+ goto err_master_put;
+ }
+
+ err = spi_register_master(master);
+ if (err) {
+ dev_err(&vdev->dev, "Cannot register master\n");
+ goto err_master_put;
+ }
+
+ /* spi_new_device() currently does not use bus_num but better set it */
+ board_info.bus_num = (u16)master->bus_num;
bus_num is not necessary actually, driver will dynamicly assign it if
bus_num is -1(initial value), besides, it's not necessary to build the
mapping relationship via bus_num.
+
+ /* Add chip selects to master device */
+ for (csi = 0; csi < master->num_chipselect; csi++) {
+ dev_info(&vdev->dev, "Setting up CS=%u\n", csi);
+ board_info.chip_select = csi;
+ if (!spi_new_device(master, &board_info)) {
+ dev_err(&vdev->dev, "Cannot setup device %u\n", csi);
+ goto err_unregister_master;
+ }
+ }
+
+ /* Request device going live */
+ virtio_device_ready(vdev); /* Optionally done by virtio_dev_probe() */
+
+ dev_info(&vdev->dev, "Device live!\n");
+
+ return 0;
+
+err_unregister_master:
+ spi_unregister_master(master);
+err_master_put:
+ spi_master_put(master);
+err_return:
+ return err;
+}
+
+static void virtio_spi_remove(struct virtio_device *vdev)
+{
+ struct spi_master *master = dev_get_drvdata(&vdev->dev);
+
+ virtio_spi_del_vq(vdev);
+ spi_unregister_master(master);
+}
+
+#ifdef CONFIG_PM_SLEEP
+/*
+ * Compare with i2c-virtio.c function virtio_i2c_freeze()
+ * and with spi-atmel.c function atmel_spi_suspend()
+ */
+static int virtio_spi_freeze(struct virtio_device *vdev)
+{
+ struct device *dev = &vdev->dev;
+ struct spi_master *master = dev_get_drvdata(dev);
+ int ret;
+
+ /* Stop the queue running */
+ ret = spi_master_suspend(master);
+ if (ret) {
+ dev_warn(dev, "cannot suspend master (%d)\n", ret);
+ return ret;
+ }
+
+ virtio_spi_del_vq(vdev);
+ return 0;
+}
+
+/*
+ * Compare with i2c-virtio.c function virtio_i2c_restore()
+ * and with spi-atmel.c function atmel_spi_resume()
+ */
+static int virtio_spi_restore(struct virtio_device *vdev)
+{
+ struct device *dev = &vdev->dev;
+ struct spi_master *master = dev_get_drvdata(dev);
+ int ret;
+
+ /* Start the queue running */
+ ret = spi_master_resume(master);
+ if (ret)
+ dev_err(dev, "problem starting queue (%d)\n", ret);
+
+ return virtio_spi_find_vqs(vdev->priv);
+}
+#endif
+
+static struct virtio_device_id virtio_spi_id_table[] = {
+ { VIRTIO_ID_SPI, VIRTIO_DEV_ANY_ID },
+ { 0 },
+};
+
+static struct virtio_driver virtio_spi_driver = {
+ .feature_table = NULL,
+ .feature_table_size = 0u,
+ .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,
+ .config_changed = NULL,
+#ifdef CONFIG_PM_SLEEP
+ .freeze = virtio_spi_freeze,
+ .restore = virtio_spi_restore,
+#endif
+};
+
+module_virtio_driver(virtio_spi_driver);
+MODULE_DEVICE_TABLE(virtio, virtio_spi_id_table);
+
+MODULE_AUTHOR("OpenSynergy GmbH");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("SPI bus driver for Virtio SPI");
Best Regards
Haixcui
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