[v1] mmc/virtio: Add virtio MMC driver for QEMU emulation

[PATCH] mmc/virtio: Add virtio MMC driver for QEMU emulation

Posted by Mikhail Krasheninnikov 1 year, 5 months ago

Introduce a new virtio MMC driver to enable virtio SD/MMC card
emulation with QEMU. This driver allows emulating MMC cards in
virtual environments, enhancing functionality and testing
capabilities within QEMU.

Link to the QEMU patch: https://lists.nongnu.org/archive/html/qemu-block/2024-06/msg00664.html

No changes to existing dependencies or documentation.

Signed-off-by: Mikhail Krasheninnikov <krashmisha@gmail.com>
CC: Ulf Hansson <ulf.hansson@linaro.org>
CC: linux-mmc@vger.kernel.org
CC: Matwey Kornilov <matwey.kornilov@gmail.com>
---
 drivers/mmc/core/mmc_ops.c      |   2 +
 drivers/mmc/host/Kconfig        |  14 ++
 drivers/mmc/host/Makefile       |   2 +
 drivers/mmc/host/virtio-mmc.c   | 266 ++++++++++++++++++++++++++++++++
 drivers/mmc/host/virtio-mmc.h   |  42 +++++
 include/uapi/linux/virtio_ids.h |   1 +
 6 files changed, 327 insertions(+)
 create mode 100644 drivers/mmc/host/virtio-mmc.c
 create mode 100644 drivers/mmc/host/virtio-mmc.h

diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index 3b3adbddf664..4e663140048a 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -5,6 +5,7 @@
  *  Copyright 2006-2007 Pierre Ossman
  */
 
+#include "linux/printk.h"
 #include <linux/slab.h>
 #include <linux/export.h>
 #include <linux/types.h>
@@ -459,6 +460,7 @@ int mmc_switch_status(struct mmc_card *card, bool crc_err_fatal)
 
 static int mmc_busy_cb(void *cb_data, bool *busy)
 {
+	pr_info("mmc_busy_cb\n");
 	struct mmc_busy_data *data = cb_data;
 	struct mmc_host *host = data->card->host;
 	u32 status = 0;
diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 554e67103c1a..eb0b0e80250d 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -1069,3 +1069,17 @@ config MMC_LITEX
 	  module will be called litex_mmc.
 
 	  If unsure, say N.
+
+config MMC_VIRTIO
+	tristate "VirtIO MMC Host Controller support"
+	depends on VIRTIO
+	help
+	  This enables support for the Virtio MMC driver, which allows the
+	  kernel to interact with MMC devices over Virtio. Virtio is a
+	  virtualization standard for network and disk device drivers,
+	  providing a common API for virtualized environments.
+
+	  Enable this option if you are running the kernel in a virtualized
+	  environment and need MMC support via Virtio.
+
+	  If unsure, say N.
\ No newline at end of file
diff --git a/drivers/mmc/host/Makefile b/drivers/mmc/host/Makefile
index a693fa3d3f1c..d53493d0a692 100644
--- a/drivers/mmc/host/Makefile
+++ b/drivers/mmc/host/Makefile
@@ -108,3 +108,5 @@ endif
 
 obj-$(CONFIG_MMC_SDHCI_XENON)	+= sdhci-xenon-driver.o
 sdhci-xenon-driver-y		+= sdhci-xenon.o sdhci-xenon-phy.o
+
+obj-$(CONFIG_MMC_VIRTIO)	+= virtio-mmc.o
\ No newline at end of file
diff --git a/drivers/mmc/host/virtio-mmc.c b/drivers/mmc/host/virtio-mmc.c
new file mode 100644
index 000000000000..b192bd0b9ffd
--- /dev/null
+++ b/drivers/mmc/host/virtio-mmc.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  VirtIO SD/MMC driver
+ *
+ *  Author: Mikhail Krasheninnikov <krashmisha@gmail.com>
+ */
+
+#include "virtio-mmc.h"
+#include "asm-generic/int-ll64.h"
+#include "linux/completion.h"
+#include "linux/kern_levels.h"
+#include "linux/mmc/core.h"
+#include "linux/mmc/host.h"
+#include "linux/printk.h"
+#include "linux/scatterlist.h"
+#include "linux/types.h"
+#include "linux/virtio_config.h"
+#include <linux/virtio.h>
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+
+struct mmc_req {
+	u32 opcode;
+	u32 arg;
+};
+
+struct virtio_mmc_request {
+	u8 flags;
+
+#define VIRTIO_MMC_REQUEST_DATA BIT(1)
+#define VIRTIO_MMC_REQUEST_WRITE BIT(2)
+#define VIRTIO_MMC_REQUEST_STOP BIT(3)
+#define VIRTIO_MMC_REQUEST_SBC BIT(4)
+
+	struct mmc_req request;
+
+	u8 buf[4096];
+	size_t buf_len;
+
+	struct mmc_req stop_req;
+	struct mmc_req sbc_req;
+};
+
+struct virtio_mmc_response {
+	u32 cmd_resp[4];
+	int cmd_resp_len;
+	u8 buf[4096];
+};
+
+struct virtio_mmc_host {
+	struct virtio_device *vdev;
+	struct mmc_host *mmc;
+	struct virtqueue *vq;
+	struct mmc_request *current_request;
+
+	struct virtio_mmc_request virtio_request;
+	struct virtio_mmc_response virtio_response;
+
+	struct completion request_handled;
+};
+
+static void virtio_mmc_vq_callback(struct virtqueue *vq)
+{
+	unsigned int len;
+	struct mmc_host *mmc;
+	struct virtio_mmc_host *host;
+	struct virtio_mmc_request *virtio_request;
+	struct virtio_mmc_response *virtio_response;
+	struct mmc_request *mrq;
+
+	mmc = vq->vdev->priv;
+	host = mmc_priv(mmc);
+	mrq = host->current_request;
+	virtio_request = &host->virtio_request;
+
+	virtio_response = virtqueue_get_buf(vq, &len);
+
+	memcpy(mrq->cmd->resp, virtio_response->cmd_resp,
+	       virtio_response->cmd_resp_len);
+
+	if (virtio_request->flags & VIRTIO_MMC_REQUEST_DATA) {
+		if (!(virtio_request->flags & VIRTIO_MMC_REQUEST_WRITE)) {
+			sg_copy_from_buffer(mrq->data->sg, mrq->data->sg_len,
+					    virtio_response->buf,
+					    virtio_request->buf_len);
+		}
+		mrq->data->bytes_xfered = virtio_request->buf_len;
+	}
+
+	host->current_request = NULL;
+	mmc_request_done(mmc, mrq);
+	complete(&host->request_handled);
+}
+
+static void virtio_mmc_send_request_to_qemu(struct virtio_mmc_host *data)
+{
+	struct scatterlist sg_out_linux, sg_in_linux;
+
+	sg_init_one(&sg_out_linux, &data->virtio_request,
+		    sizeof(struct virtio_mmc_request));
+	sg_init_one(&sg_in_linux, &data->virtio_response,
+		    sizeof(struct virtio_mmc_response));
+
+	struct scatterlist *request[] = { &sg_out_linux, &sg_in_linux };
+
+	if (virtqueue_add_sgs(data->vq, request, 1, 1, &data->virtio_response,
+			      GFP_KERNEL) < 0) {
+		dev_crit(&data->vdev->dev, "virtio_mmc: Failed to add sg\n");
+		return;
+	}
+
+	virtqueue_kick(data->vq);
+	wait_for_completion(&data->request_handled);
+}
+
+static inline size_t __calculate_len(struct mmc_data *data)
+{
+	size_t len = 0;
+
+	for (int i = 0; i < data->sg_len; i++)
+		len += data->sg[i].length;
+	return len;
+}
+
+/* MMC layer callbacks */
+
+static void virtio_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
+{
+	struct virtio_mmc_host *host;
+	struct virtio_mmc_request *virtio_req;
+	struct mmc_data *mrq_data;
+
+	host = mmc_priv(mmc);
+	host->current_request = mrq; // Saving the request for the callback
+
+	virtio_req = &host->virtio_request;
+	memset(virtio_req, 0, sizeof(struct virtio_mmc_request));
+
+	virtio_req->request.opcode = mrq->cmd->opcode;
+	virtio_req->request.arg = mrq->cmd->arg;
+
+	mrq_data = mrq->data;
+	if (mrq_data) {
+		virtio_req->flags |= VIRTIO_MMC_REQUEST_DATA;
+
+		virtio_req->buf_len = __calculate_len(mrq->data);
+
+		virtio_req->flags |= ((mrq_data->flags & MMC_DATA_WRITE) ?
+					      VIRTIO_MMC_REQUEST_WRITE :
+					      0);
+		if (virtio_req->flags & VIRTIO_MMC_REQUEST_WRITE) {
+			sg_copy_to_buffer(mrq_data->sg, mrq_data->sg_len,
+					  virtio_req->buf, virtio_req->buf_len);
+		}
+	}
+
+	if (mrq->stop) {
+		virtio_req->flags |= VIRTIO_MMC_REQUEST_STOP;
+
+		virtio_req->stop_req.opcode = mrq->stop->opcode;
+		virtio_req->stop_req.arg = mrq->stop->arg;
+	}
+
+	if (mrq->sbc) {
+		virtio_req->flags |= VIRTIO_MMC_REQUEST_SBC;
+
+		virtio_req->sbc_req.opcode = mrq->sbc->opcode;
+		virtio_req->sbc_req.arg = mrq->sbc->arg;
+	}
+
+	virtio_mmc_send_request_to_qemu(host);
+}
+
+static void virtio_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
+{
+}
+
+static int virtio_mmc_get_ro(struct mmc_host *mmc)
+{
+	return 0;
+}
+
+static int virtio_mmc_get_cd(struct mmc_host *mmc)
+{
+	return 1;
+}
+
+static const struct mmc_host_ops virtio_mmc_host_ops = {
+	.request = virtio_mmc_request,
+	.set_ios = virtio_mmc_set_ios,
+	.get_ro = virtio_mmc_get_ro,
+	.get_cd = virtio_mmc_get_cd,
+};
+
+static inline void __fill_host_attr(struct mmc_host *host)
+{
+	host->ops = &virtio_mmc_host_ops;
+	host->f_min = 300000;
+	host->f_max = 500000;
+	host->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
+	host->caps = MMC_CAP_SD_HIGHSPEED;
+	host->caps2 = MMC_CAP2_NO_SDIO | MMC_CAP2_NO_MMC | MMC_CAP2_HS400;
+}
+
+static int create_host(struct virtio_device *vdev)
+{
+	int err;
+	struct mmc_host *mmc;
+	struct virtio_mmc_host *host;
+
+	mmc = mmc_alloc_host(sizeof(struct virtio_mmc_host), &vdev->dev);
+	if (!mmc) {
+		pr_err("virtio_mmc: Failed to allocate host\n");
+		return -ENOMEM;
+	}
+
+	__fill_host_attr(mmc);
+
+	vdev->priv = mmc;
+
+	host = mmc_priv(mmc);
+
+	init_completion(&host->request_handled);
+
+	host->vq =
+		virtio_find_single_vq(vdev, virtio_mmc_vq_callback, "vq_name");
+	if (!host->vq) {
+		pr_err("virtio_mmc: Failed to find virtqueue\n");
+		mmc_free_host(mmc);
+		return -ENODEV;
+	}
+
+	err = mmc_add_host(mmc);
+	if (err) {
+		pr_err("virtio_mmc: Failed to add host\n");
+		mmc_free_host(mmc);
+		return err;
+	}
+
+	return 0;
+}
+
+static int virtio_mmc_probe(struct virtio_device *vdev)
+{
+	int err;
+
+	err = create_host(vdev);
+	if (err)
+		pr_err("virtio_mmc: Failed to make host\n");
+
+	return 0;
+}
+
+static void remove_host(struct mmc_host *host)
+{
+	mmc_remove_host(host);
+	mmc_free_host(host);
+}
+
+static void virtio_mmc_remove(struct virtio_device *vdev)
+{
+	struct mmc_host *host = vdev->priv;
+
+	remove_host(host);
+}
diff --git a/drivers/mmc/host/virtio-mmc.h b/drivers/mmc/host/virtio-mmc.h
new file mode 100644
index 000000000000..086f33307f84
--- /dev/null
+++ b/drivers/mmc/host/virtio-mmc.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ *  VirtIO SD/MMC driver
+ *
+ *  Author: Mikhail Krasheninnikov <krashmisha@gmail.com>
+ */
+
+#ifndef _VIRTIO_MMC_H
+#define _VIRTIO_MMC_H
+
+#include <linux/virtio.h>
+#include <linux/virtio_ids.h>
+
+#define VIRTIO_MMC_DEV_ID 42
+
+static int virtio_mmc_probe(struct virtio_device *vdev);
+
+static void virtio_mmc_remove(struct virtio_device *vdev);
+
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_MMC_DEV_ID, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+static struct virtio_driver virtio_mmc_driver = {
+	.driver = {
+		.name	= KBUILD_MODNAME,
+		.owner	= THIS_MODULE,
+	},
+	.id_table	= id_table,
+	.probe		= virtio_mmc_probe,
+	.remove		= virtio_mmc_remove,
+};
+
+module_virtio_driver(virtio_mmc_driver);
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+MODULE_AUTHOR("Mikhail Krasheninnikov");
+MODULE_DESCRIPTION("VirtIO SD/MMC driver");
+MODULE_LICENSE("GPL");
+
+#endif
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index 7aa2eb766205..9c8a09b0f004 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -68,6 +68,7 @@
 #define VIRTIO_ID_AUDIO_POLICY		39 /* virtio audio policy */
 #define VIRTIO_ID_BT			40 /* virtio bluetooth */
 #define VIRTIO_ID_GPIO			41 /* virtio gpio */
+#define VIRTIO_ID_MMC           42 /* virtio mmc */
 
 /*
  * Virtio Transitional IDs
-- 
2.34.1

Re: [PATCH] mmc/virtio: Add virtio MMC driver for QEMU emulation

Posted by Michael S. Tsirkin 1 year, 5 months ago

On Mon, Jul 01, 2024 at 12:06:42PM +0000, Mikhail Krasheninnikov wrote:
> Introduce a new virtio MMC driver to enable virtio SD/MMC card
> emulation with QEMU. This driver allows emulating MMC cards in
> virtual environments, enhancing functionality and testing
> capabilities within QEMU.
> 
> Link to the QEMU patch: https://lists.nongnu.org/archive/html/qemu-block/2024-06/msg00664.html
> 
> No changes to existing dependencies or documentation.
> 
> Signed-off-by: Mikhail Krasheninnikov <krashmisha@gmail.com>
> CC: Ulf Hansson <ulf.hansson@linaro.org>
> CC: linux-mmc@vger.kernel.org
> CC: Matwey Kornilov <matwey.kornilov@gmail.com>


you should likely add a MAINTAINERS entry so people
know to copy virtio ML and core maintainers when they are
making changes.

> ---
>  drivers/mmc/core/mmc_ops.c      |   2 +
>  drivers/mmc/host/Kconfig        |  14 ++
>  drivers/mmc/host/Makefile       |   2 +
>  drivers/mmc/host/virtio-mmc.c   | 266 ++++++++++++++++++++++++++++++++
>  drivers/mmc/host/virtio-mmc.h   |  42 +++++
>  include/uapi/linux/virtio_ids.h |   1 +
>  6 files changed, 327 insertions(+)
>  create mode 100644 drivers/mmc/host/virtio-mmc.c
>  create mode 100644 drivers/mmc/host/virtio-mmc.h
> 
> diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
> index 3b3adbddf664..4e663140048a 100644
> --- a/drivers/mmc/core/mmc_ops.c
> +++ b/drivers/mmc/core/mmc_ops.c
> @@ -5,6 +5,7 @@
>   *  Copyright 2006-2007 Pierre Ossman
>   */
>  
> +#include "linux/printk.h"
>  #include <linux/slab.h>
>  #include <linux/export.h>
>  #include <linux/types.h>
> @@ -459,6 +460,7 @@ int mmc_switch_status(struct mmc_card *card, bool crc_err_fatal)
>  
>  static int mmc_busy_cb(void *cb_data, bool *busy)
>  {
> +	pr_info("mmc_busy_cb\n");
>  	struct mmc_busy_data *data = cb_data;
>  	struct mmc_host *host = data->card->host;
>  	u32 status = 0;


Debugging leftovers? Does not inspire confidence...


> diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
> index 554e67103c1a..eb0b0e80250d 100644
> --- a/drivers/mmc/host/Kconfig
> +++ b/drivers/mmc/host/Kconfig
> @@ -1069,3 +1069,17 @@ config MMC_LITEX
>  	  module will be called litex_mmc.
>  
>  	  If unsure, say N.
> +
> +config MMC_VIRTIO
> +	tristate "VirtIO MMC Host Controller support"
> +	depends on VIRTIO
> +	help
> +	  This enables support for the Virtio MMC driver, which allows the
> +	  kernel to interact with MMC devices over Virtio. Virtio is a
> +	  virtualization standard for network and disk device drivers,
> +	  providing a common API for virtualized environments.
> +
> +	  Enable this option if you are running the kernel in a virtualized
> +	  environment and need MMC support via Virtio.
> +
> +	  If unsure, say N.
> \ No newline at end of file
> diff --git a/drivers/mmc/host/Makefile b/drivers/mmc/host/Makefile
> index a693fa3d3f1c..d53493d0a692 100644
> --- a/drivers/mmc/host/Makefile
> +++ b/drivers/mmc/host/Makefile
> @@ -108,3 +108,5 @@ endif
>  
>  obj-$(CONFIG_MMC_SDHCI_XENON)	+= sdhci-xenon-driver.o
>  sdhci-xenon-driver-y		+= sdhci-xenon.o sdhci-xenon-phy.o
> +
> +obj-$(CONFIG_MMC_VIRTIO)	+= virtio-mmc.o
> \ No newline at end of file
> diff --git a/drivers/mmc/host/virtio-mmc.c b/drivers/mmc/host/virtio-mmc.c
> new file mode 100644
> index 000000000000..b192bd0b9ffd
> --- /dev/null
> +++ b/drivers/mmc/host/virtio-mmc.c
> @@ -0,0 +1,266 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + *  VirtIO SD/MMC driver
> + *
> + *  Author: Mikhail Krasheninnikov <krashmisha@gmail.com>
> + */
> +
> +#include "virtio-mmc.h"
> +#include "asm-generic/int-ll64.h"
> +#include "linux/completion.h"
> +#include "linux/kern_levels.h"
> +#include "linux/mmc/core.h"
> +#include "linux/mmc/host.h"
> +#include "linux/printk.h"
> +#include "linux/scatterlist.h"
> +#include "linux/types.h"
> +#include "linux/virtio_config.h"
> +#include <linux/virtio.h>
> +#include <linux/cdev.h>
> +#include <linux/device.h>
> +#include <linux/fs.h>

why this weird order and way to do includes?
and it looks like you are including way too much stuff.

> +
> +struct mmc_req {
> +	u32 opcode;
> +	u32 arg;

Using CPU endian format for driver to device communication
is not a good idea.

> +};
> +
> +struct virtio_mmc_request {
> +	u8 flags;
> +
> +#define VIRTIO_MMC_REQUEST_DATA BIT(1)
> +#define VIRTIO_MMC_REQUEST_WRITE BIT(2)
> +#define VIRTIO_MMC_REQUEST_STOP BIT(3)
> +#define VIRTIO_MMC_REQUEST_SBC BIT(4)
> +
> +	struct mmc_req request;
> +
> +	u8 buf[4096];
> +	size_t buf_len;

size_t is definitely not a good idea in a driver to device
communication.

> +
> +	struct mmc_req stop_req;
> +	struct mmc_req sbc_req;
> +};
> +
> +struct virtio_mmc_response {
> +	u32 cmd_resp[4];

> +	int cmd_resp_len;

int is also not a good idea in a driver to device communication.


> +	u8 buf[4096];
> +};


looks like there's a bunch of stuff here that belongs in
uapi/linux/virtio-mmc.h (or whatever you decide to name this).

> +
> +struct virtio_mmc_host {
> +	struct virtio_device *vdev;
> +	struct mmc_host *mmc;
> +	struct virtqueue *vq;
> +	struct mmc_request *current_request;
> +
> +	struct virtio_mmc_request virtio_request;
> +	struct virtio_mmc_response virtio_response;
> +
> +	struct completion request_handled;
> +};
> +
> +static void virtio_mmc_vq_callback(struct virtqueue *vq)
> +{
> +	unsigned int len;
> +	struct mmc_host *mmc;
> +	struct virtio_mmc_host *host;
> +	struct virtio_mmc_request *virtio_request;
> +	struct virtio_mmc_response *virtio_response;
> +	struct mmc_request *mrq;
> +
> +	mmc = vq->vdev->priv;
> +	host = mmc_priv(mmc);
> +	mrq = host->current_request;
> +	virtio_request = &host->virtio_request;
> +
> +	virtio_response = virtqueue_get_buf(vq, &len);
> +
> +	memcpy(mrq->cmd->resp, virtio_response->cmd_resp,
> +	       virtio_response->cmd_resp_len);

blindly trusting device that cmd_resp_len will not overflow
the buffer is not a good idea.


> +
> +	if (virtio_request->flags & VIRTIO_MMC_REQUEST_DATA) {
> +		if (!(virtio_request->flags & VIRTIO_MMC_REQUEST_WRITE)) {
> +			sg_copy_from_buffer(mrq->data->sg, mrq->data->sg_len,
> +					    virtio_response->buf,
> +					    virtio_request->buf_len);
> +		}
> +		mrq->data->bytes_xfered = virtio_request->buf_len;

same here - validate it's reasonable


> +	}
> +
> +	host->current_request = NULL;
> +	mmc_request_done(mmc, mrq);
> +	complete(&host->request_handled);
> +}
> +
> +static void virtio_mmc_send_request_to_qemu(struct virtio_mmc_host *data)
> +{
> +	struct scatterlist sg_out_linux, sg_in_linux;
> +
> +	sg_init_one(&sg_out_linux, &data->virtio_request,
> +		    sizeof(struct virtio_mmc_request));
> +	sg_init_one(&sg_in_linux, &data->virtio_response,
> +		    sizeof(struct virtio_mmc_response));
> +
> +	struct scatterlist *request[] = { &sg_out_linux, &sg_in_linux };
> +
> +	if (virtqueue_add_sgs(data->vq, request, 1, 1, &data->virtio_response,
> +			      GFP_KERNEL) < 0) {
> +		dev_crit(&data->vdev->dev, "virtio_mmc: Failed to add sg\n");
> +		return;
> +	}
> +
> +	virtqueue_kick(data->vq);
> +	wait_for_completion(&data->request_handled);
> +}
> +
> +static inline size_t __calculate_len(struct mmc_data *data)
> +{
> +	size_t len = 0;
> +
> +	for (int i = 0; i < data->sg_len; i++)
> +		len += data->sg[i].length;
> +	return len;
> +}
> +
> +/* MMC layer callbacks */
> +
> +static void virtio_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
> +{
> +	struct virtio_mmc_host *host;
> +	struct virtio_mmc_request *virtio_req;
> +	struct mmc_data *mrq_data;
> +
> +	host = mmc_priv(mmc);
> +	host->current_request = mrq; // Saving the request for the callback

no locking anywhere ...
does something else guarantee there's always just one request
outstanding?


> +
> +	virtio_req = &host->virtio_request;
> +	memset(virtio_req, 0, sizeof(struct virtio_mmc_request));
> +
> +	virtio_req->request.opcode = mrq->cmd->opcode;
> +	virtio_req->request.arg = mrq->cmd->arg;
> +
> +	mrq_data = mrq->data;
> +	if (mrq_data) {
> +		virtio_req->flags |= VIRTIO_MMC_REQUEST_DATA;
> +
> +		virtio_req->buf_len = __calculate_len(mrq->data);
> +
> +		virtio_req->flags |= ((mrq_data->flags & MMC_DATA_WRITE) ?
> +					      VIRTIO_MMC_REQUEST_WRITE :
> +					      0);
> +		if (virtio_req->flags & VIRTIO_MMC_REQUEST_WRITE) {
> +			sg_copy_to_buffer(mrq_data->sg, mrq_data->sg_len,
> +					  virtio_req->buf, virtio_req->buf_len);
> +		}
> +	}
> +
> +	if (mrq->stop) {
> +		virtio_req->flags |= VIRTIO_MMC_REQUEST_STOP;
> +
> +		virtio_req->stop_req.opcode = mrq->stop->opcode;
> +		virtio_req->stop_req.arg = mrq->stop->arg;
> +	}
> +
> +	if (mrq->sbc) {
> +		virtio_req->flags |= VIRTIO_MMC_REQUEST_SBC;
> +
> +		virtio_req->sbc_req.opcode = mrq->sbc->opcode;
> +		virtio_req->sbc_req.arg = mrq->sbc->arg;
> +	}
> +
> +	virtio_mmc_send_request_to_qemu(host);
> +}
> +
> +static void virtio_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> +{
> +}
> +
> +static int virtio_mmc_get_ro(struct mmc_host *mmc)
> +{
> +	return 0;
> +}
> +
> +static int virtio_mmc_get_cd(struct mmc_host *mmc)
> +{
> +	return 1;
> +}
> +
> +static const struct mmc_host_ops virtio_mmc_host_ops = {
> +	.request = virtio_mmc_request,
> +	.set_ios = virtio_mmc_set_ios,
> +	.get_ro = virtio_mmc_get_ro,
> +	.get_cd = virtio_mmc_get_cd,
> +};
> +
> +static inline void __fill_host_attr(struct mmc_host *host)
> +{
> +	host->ops = &virtio_mmc_host_ops;
> +	host->f_min = 300000;
> +	host->f_max = 500000;
> +	host->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
> +	host->caps = MMC_CAP_SD_HIGHSPEED;
> +	host->caps2 = MMC_CAP2_NO_SDIO | MMC_CAP2_NO_MMC | MMC_CAP2_HS400;
> +}
> +
> +static int create_host(struct virtio_device *vdev)
> +{
> +	int err;
> +	struct mmc_host *mmc;
> +	struct virtio_mmc_host *host;
> +
> +	mmc = mmc_alloc_host(sizeof(struct virtio_mmc_host), &vdev->dev);
> +	if (!mmc) {
> +		pr_err("virtio_mmc: Failed to allocate host\n");
> +		return -ENOMEM;
> +	}
> +
> +	__fill_host_attr(mmc);
> +
> +	vdev->priv = mmc;
> +
> +	host = mmc_priv(mmc);
> +
> +	init_completion(&host->request_handled);
> +
> +	host->vq =
> +		virtio_find_single_vq(vdev, virtio_mmc_vq_callback, "vq_name");
> +	if (!host->vq) {
> +		pr_err("virtio_mmc: Failed to find virtqueue\n");
> +		mmc_free_host(mmc);
> +		return -ENODEV;
> +	}
> +
> +	err = mmc_add_host(mmc);


can you get requests immediately at this point?
if yes you need to call virtio_device_ready before
you add buffers.

> +	if (err) {
> +		pr_err("virtio_mmc: Failed to add host\n");
> +		mmc_free_host(mmc);
> +		return err;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtio_mmc_probe(struct virtio_device *vdev)
> +{
> +	int err;
> +
> +	err = create_host(vdev);
> +	if (err)
> +		pr_err("virtio_mmc: Failed to make host\n");
> +
> +	return 0;
> +}
> +
> +static void remove_host(struct mmc_host *host)
> +{

does not look like you are doing anything to quiesce the
device.


> +	mmc_remove_host(host);
> +	mmc_free_host(host);
> +}
> +
> +static void virtio_mmc_remove(struct virtio_device *vdev)
> +{
> +	struct mmc_host *host = vdev->priv;
> +
> +	remove_host(host);
> +}
> diff --git a/drivers/mmc/host/virtio-mmc.h b/drivers/mmc/host/virtio-mmc.h
> new file mode 100644
> index 000000000000..086f33307f84
> --- /dev/null
> +++ b/drivers/mmc/host/virtio-mmc.h
> @@ -0,0 +1,42 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later
> + *
> + *  VirtIO SD/MMC driver
> + *
> + *  Author: Mikhail Krasheninnikov <krashmisha@gmail.com>
> + */
> +
> +#ifndef _VIRTIO_MMC_H
> +#define _VIRTIO_MMC_H
> +
> +#include <linux/virtio.h>
> +#include <linux/virtio_ids.h>
> +
> +#define VIRTIO_MMC_DEV_ID 42
> +
> +static int virtio_mmc_probe(struct virtio_device *vdev);
> +
> +static void virtio_mmc_remove(struct virtio_device *vdev);
> +
> +static const struct virtio_device_id id_table[] = {
> +	{ VIRTIO_MMC_DEV_ID, VIRTIO_DEV_ANY_ID },
> +	{ 0 },
> +};
> +
> +static struct virtio_driver virtio_mmc_driver = {
> +	.driver = {
> +		.name	= KBUILD_MODNAME,
> +		.owner	= THIS_MODULE,
> +	},
> +	.id_table	= id_table,
> +	.probe		= virtio_mmc_probe,
> +	.remove		= virtio_mmc_remove,
> +};
> +
> +module_virtio_driver(virtio_mmc_driver);
> +MODULE_DEVICE_TABLE(virtio, id_table);
> +
> +MODULE_AUTHOR("Mikhail Krasheninnikov");
> +MODULE_DESCRIPTION("VirtIO SD/MMC driver");
> +MODULE_LICENSE("GPL");
> +
> +#endif
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 7aa2eb766205..9c8a09b0f004 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -68,6 +68,7 @@
>  #define VIRTIO_ID_AUDIO_POLICY		39 /* virtio audio policy */
>  #define VIRTIO_ID_BT			40 /* virtio bluetooth */
>  #define VIRTIO_ID_GPIO			41 /* virtio gpio */
> +#define VIRTIO_ID_MMC           42 /* virtio mmc */
>  
>  /*
>   * Virtio Transitional IDs
> -- 
> 2.34.1
>