diff mbox series

[v4,8/8] virtio: rng: Add a random number generator(rng) driver

Message ID 1576583525-3817-9-git-send-email-sughosh.ganu@linaro.org
State Superseded, archived
Headers show
Series Add a random number generator uclass | expand

Commit Message

Sughosh Ganu Dec. 17, 2019, 11:52 a.m. UTC 
Add a driver for the virtio-rng device on the qemu platform. The
device uses pci as a transport medium. The driver can be enabled with
the following configs

CONFIG_VIRTIO
CONFIG_DM_RNG
CONFIG_VIRTIO_PCI
CONFIG_VIRTIO_RNG

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
---
 drivers/virtio/Kconfig         |  6 ++++
 drivers/virtio/Makefile        |  1 +
 drivers/virtio/virtio-uclass.c |  1 +
 drivers/virtio/virtio_rng.c    | 72 ++++++++++++++++++++++++++++++++++++++++++
 include/virtio.h               |  4 ++-
 5 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 drivers/virtio/virtio_rng.c

Comments

Heinrich Schuchardt Dec. 24, 2019, 9:39 p.m. UTC | #1 
On 12/17/19 12:52 PM, Sughosh Ganu wrote:
> Add a driver for the virtio-rng device on the qemu platform. The
> device uses pci as a transport medium. The driver can be enabled with
> the following configs
>
> CONFIG_VIRTIO
> CONFIG_DM_RNG
> CONFIG_VIRTIO_PCI
> CONFIG_VIRTIO_RNG
>
> Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> ---
>   drivers/virtio/Kconfig         |  6 ++++
>   drivers/virtio/Makefile        |  1 +
>   drivers/virtio/virtio-uclass.c |  1 +
>   drivers/virtio/virtio_rng.c    | 72 ++++++++++++++++++++++++++++++++++++++++++
>   include/virtio.h               |  4 ++-
>   5 files changed, 83 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/virtio/virtio_rng.c
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index a9d5fd0..2e3dd3b 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -59,4 +59,10 @@ config VIRTIO_BLK
>   	  This is the virtual block driver for virtio. It can be used with
>   	  QEMU based targets.
>
> +config VIRTIO_RNG
> +       bool "virtio rng driver"
> +       depends on VIRTIO
> +       help
> +         This is the virtual random number generator driver. It can be used
> +	 with Qemu based targets.
>   endmenu
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 4579044..dc88809 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -9,3 +9,4 @@ obj-$(CONFIG_VIRTIO_PCI) += virtio_pci_legacy.o virtio_pci_modern.o
>   obj-$(CONFIG_VIRTIO_SANDBOX) += virtio_sandbox.o
>   obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
>   obj-$(CONFIG_VIRTIO_BLK) += virtio_blk.o
> +obj-$(CONFIG_VIRTIO_RNG) += virtio_rng.o
> diff --git a/drivers/virtio/virtio-uclass.c b/drivers/virtio/virtio-uclass.c
> index 34397d7..436faa4 100644
> --- a/drivers/virtio/virtio-uclass.c
> +++ b/drivers/virtio/virtio-uclass.c
> @@ -24,6 +24,7 @@
>   static const char *const virtio_drv_name[VIRTIO_ID_MAX_NUM] = {
>   	[VIRTIO_ID_NET]		= VIRTIO_NET_DRV_NAME,
>   	[VIRTIO_ID_BLOCK]	= VIRTIO_BLK_DRV_NAME,
> +	[VIRTIO_ID_RNG]		= VIRTIO_RNG_DRV_NAME,
>   };
>
>   int virtio_get_config(struct udevice *vdev, unsigned int offset,
> diff --git a/drivers/virtio/virtio_rng.c b/drivers/virtio/virtio_rng.c
> new file mode 100644
> index 0000000..19a0cc1
> --- /dev/null
> +++ b/drivers/virtio/virtio_rng.c
> @@ -0,0 +1,72 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (c) 2019, Linaro Limited
> + */
> +
> +#include <common.h>
> +#include <dm.h>
> +#include <rng.h>
> +#include <virtio_types.h>
> +#include <virtio.h>
> +#include <virtio_ring.h>
> +
> +struct virtio_rng_priv {
> +	struct virtqueue *rng_vq;
> +};
> +
> +static int virtio_rng_read(struct udevice *dev, void *data, size_t len)
> +{
> +	struct virtio_sg sg = { data, len };
> +	struct virtio_sg *sgs[] = { &sg };
> +	struct virtio_rng_priv *priv = dev_get_priv(dev);
> +	unsigned int rsize;
> +	int ret;
> +
> +	ret = virtqueue_add(priv->rng_vq, sgs, 0, 1);
> +	if (ret)

Please, add a debug statement for each error path, e.g.

		debug("%s: virtqueue_add() failed\n", __func__)

> +		return ret;
> +
> +	virtqueue_kick(priv->rng_vq);
> +
> +	while (!virtqueue_get_buf(priv->rng_vq, &rsize))
> +		;
> +
> +	return rsize;

The return value is inconsistent with sandbox_rng_read() and
stm32_rng_read(). Both return 0 on success.

With "return 0;" the driver works fine.

> +}
> +
> +static int virtio_rng_bind(struct udevice *dev)
> +{
> +	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(dev->parent);
> +
> +	/* Indicate what driver features we support */
> +	virtio_driver_features_init(uc_priv, NULL, 0, NULL, 0);
> +
> +	return 0;
> +}
> +
> +static int virtio_rng_probe(struct udevice *dev)
> +{
> +	struct virtio_rng_priv *priv = dev_get_priv(dev);
> +	int ret;
> +
> +	ret = virtio_find_vqs(dev, 1, &priv->rng_vq);
> +	if (ret < 0)

Add a debug statement here, please, e.g.

		debug("%s: virtio_find_vqs() failed\n", __func__)

Best regards

Heinrich

> +		return ret;
> +
> +	return 0;
> +}
> +
> +static const struct dm_rng_ops virtio_rng_ops = {
> +	.read	= virtio_rng_read,
> +};
> +
> +U_BOOT_DRIVER(virtio_rng) = {
> +	.name	= VIRTIO_RNG_DRV_NAME,
> +	.id	= UCLASS_RNG,
> +	.bind	= virtio_rng_bind,
> +	.probe	= virtio_rng_probe,
> +	.remove = virtio_reset,
> +	.ops	= &virtio_rng_ops,
> +	.priv_auto_alloc_size = sizeof(struct virtio_rng_priv),
> +	.flags	= DM_FLAG_ACTIVE_DMA,
> +};
> diff --git a/include/virtio.h b/include/virtio.h
> index 654fdf1..561dcc3 100644
> --- a/include/virtio.h
> +++ b/include/virtio.h
> @@ -22,10 +22,12 @@
>
>   #define VIRTIO_ID_NET		1 /* virtio net */
>   #define VIRTIO_ID_BLOCK		2 /* virtio block */
> -#define VIRTIO_ID_MAX_NUM	3
> +#define VIRTIO_ID_RNG		4 /* virtio rng */
> +#define VIRTIO_ID_MAX_NUM	5
>
>   #define VIRTIO_NET_DRV_NAME	"virtio-net"
>   #define VIRTIO_BLK_DRV_NAME	"virtio-blk"
> +#define VIRTIO_RNG_DRV_NAME	"virtio-rng"
>
>   /* Status byte for guest to report progress, and synchronize features */
>
>
Heinrich Schuchardt Dec. 25, 2019, 1:30 a.m. UTC | #2 
On 12/24/19 10:39 PM, Heinrich Schuchardt wrote:
> On 12/17/19 12:52 PM, Sughosh Ganu wrote:
>> Add a driver for the virtio-rng device on the qemu platform. The
>> device uses pci as a transport medium. The driver can be enabled with
>> the following configs
>>
>> CONFIG_VIRTIO
>> CONFIG_DM_RNG
>> CONFIG_VIRTIO_PCI
>> CONFIG_VIRTIO_RNG
>>
>> Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
>> ---
>>   drivers/virtio/Kconfig         |  6 ++++
>>   drivers/virtio/Makefile        |  1 +
>>   drivers/virtio/virtio-uclass.c |  1 +
>>   drivers/virtio/virtio_rng.c    | 72
>> ++++++++++++++++++++++++++++++++++++++++++
>>   include/virtio.h               |  4 ++-
>>   5 files changed, 83 insertions(+), 1 deletion(-)
>>   create mode 100644 drivers/virtio/virtio_rng.c
>>
>> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
>> index a9d5fd0..2e3dd3b 100644
>> --- a/drivers/virtio/Kconfig
>> +++ b/drivers/virtio/Kconfig
>> @@ -59,4 +59,10 @@ config VIRTIO_BLK
>>         This is the virtual block driver for virtio. It can be used with
>>         QEMU based targets.
>>
>> +config VIRTIO_RNG
>> +       bool "virtio rng driver"
>> +       depends on VIRTIO
>> +       help
>> +         This is the virtual random number generator driver. It can
>> be used
>> +     with Qemu based targets.
>>   endmenu
>> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
>> index 4579044..dc88809 100644
>> --- a/drivers/virtio/Makefile
>> +++ b/drivers/virtio/Makefile
>> @@ -9,3 +9,4 @@ obj-$(CONFIG_VIRTIO_PCI) += virtio_pci_legacy.o
>> virtio_pci_modern.o
>>   obj-$(CONFIG_VIRTIO_SANDBOX) += virtio_sandbox.o
>>   obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
>>   obj-$(CONFIG_VIRTIO_BLK) += virtio_blk.o
>> +obj-$(CONFIG_VIRTIO_RNG) += virtio_rng.o
>> diff --git a/drivers/virtio/virtio-uclass.c
>> b/drivers/virtio/virtio-uclass.c
>> index 34397d7..436faa4 100644
>> --- a/drivers/virtio/virtio-uclass.c
>> +++ b/drivers/virtio/virtio-uclass.c
>> @@ -24,6 +24,7 @@
>>   static const char *const virtio_drv_name[VIRTIO_ID_MAX_NUM] = {
>>       [VIRTIO_ID_NET]        = VIRTIO_NET_DRV_NAME,
>>       [VIRTIO_ID_BLOCK]    = VIRTIO_BLK_DRV_NAME,
>> +    [VIRTIO_ID_RNG]        = VIRTIO_RNG_DRV_NAME,
>>   };
>>
>>   int virtio_get_config(struct udevice *vdev, unsigned int offset,
>> diff --git a/drivers/virtio/virtio_rng.c b/drivers/virtio/virtio_rng.c
>> new file mode 100644
>> index 0000000..19a0cc1
>> --- /dev/null
>> +++ b/drivers/virtio/virtio_rng.c
>> @@ -0,0 +1,72 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Copyright (c) 2019, Linaro Limited
>> + */
>> +
>> +#include <common.h>
>> +#include <dm.h>
>> +#include <rng.h>
>> +#include <virtio_types.h>
>> +#include <virtio.h>
>> +#include <virtio_ring.h>
>> +
>> +struct virtio_rng_priv {
>> +    struct virtqueue *rng_vq;
>> +};
>> +
>> +static int virtio_rng_read(struct udevice *dev, void *data, size_t len)
>> +{
>> +    struct virtio_sg sg = { data, len };
>> +    struct virtio_sg *sgs[] = { &sg };
>> +    struct virtio_rng_priv *priv = dev_get_priv(dev);
>> +    unsigned int rsize;
>> +    int ret;
>> +
>> +    ret = virtqueue_add(priv->rng_vq, sgs, 0, 1);
>> +    if (ret)
>
> Please, add a debug statement for each error path, e.g.
>
>          debug("%s: virtqueue_add() failed\n", __func__)
>
>> +        return ret;
>> +
>> +    virtqueue_kick(priv->rng_vq);
>> +
>> +    while (!virtqueue_get_buf(priv->rng_vq, &rsize))
>> +        ;
>> +
>> +    return rsize;
>
> The return value is inconsistent with sandbox_rng_read() and
> stm32_rng_read(). Both return 0 on success.
>
> With "return 0;" the driver works fine.

I retested with
-device virtio-rng-pci,disable-legacy=on,max-bytes=16,period=1000

In this case virtqueue_get_buf() only returns a maximum of 16 bytes. All
other bytes of data remain unchanged. If the next call occurs within
1000 milli-seconds virtqueue_get_buf() blocks until the period is over.

So either you have to change the definition of the return parameter in
patch 1/8 (and change the other drivers accordingly) or you have to add
a loop to this driver that loops until len random bytes have been retrieved.

I would prefer to add a loop in the driver instead of adding a loop in
every consumer.

Best regards

Heinrich

>
>> +}
>> +
>> +static int virtio_rng_bind(struct udevice *dev)
>> +{
>> +    struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(dev->parent);
>> +
>> +    /* Indicate what driver features we support */
>> +    virtio_driver_features_init(uc_priv, NULL, 0, NULL, 0);
>> +
>> +    return 0;
>> +}
>> +
>> +static int virtio_rng_probe(struct udevice *dev)
>> +{
>> +    struct virtio_rng_priv *priv = dev_get_priv(dev);
>> +    int ret;
>> +
>> +    ret = virtio_find_vqs(dev, 1, &priv->rng_vq);
>> +    if (ret < 0)
>
> Add a debug statement here, please, e.g.
>
>          debug("%s: virtio_find_vqs() failed\n", __func__)
>
> Best regards
>
> Heinrich
>
>> +        return ret;
>> +
>> +    return 0;
>> +}
>> +
>> +static const struct dm_rng_ops virtio_rng_ops = {
>> +    .read    = virtio_rng_read,
>> +};
>> +
>> +U_BOOT_DRIVER(virtio_rng) = {
>> +    .name    = VIRTIO_RNG_DRV_NAME,
>> +    .id    = UCLASS_RNG,
>> +    .bind    = virtio_rng_bind,
>> +    .probe    = virtio_rng_probe,
>> +    .remove = virtio_reset,
>> +    .ops    = &virtio_rng_ops,
>> +    .priv_auto_alloc_size = sizeof(struct virtio_rng_priv),
>> +    .flags    = DM_FLAG_ACTIVE_DMA,
>> +};
>> diff --git a/include/virtio.h b/include/virtio.h
>> index 654fdf1..561dcc3 100644
>> --- a/include/virtio.h
>> +++ b/include/virtio.h
>> @@ -22,10 +22,12 @@
>>
>>   #define VIRTIO_ID_NET        1 /* virtio net */
>>   #define VIRTIO_ID_BLOCK        2 /* virtio block */
>> -#define VIRTIO_ID_MAX_NUM    3
>> +#define VIRTIO_ID_RNG        4 /* virtio rng */
>> +#define VIRTIO_ID_MAX_NUM    5
>>
>>   #define VIRTIO_NET_DRV_NAME    "virtio-net"
>>   #define VIRTIO_BLK_DRV_NAME    "virtio-blk"
>> +#define VIRTIO_RNG_DRV_NAME    "virtio-rng"
>>
>>   /* Status byte for guest to report progress, and synchronize
>> features */
>>
>>
>
>
Sughosh Ganu Dec. 26, 2019, 5:35 p.m. UTC | #3 
On Wed, 25 Dec 2019 at 07:00, Heinrich Schuchardt <xypron.glpk@gmx.de>
wrote:

> On 12/24/19 10:39 PM, Heinrich Schuchardt wrote:
> > On 12/17/19 12:52 PM, Sughosh Ganu wrote:
> >> Add a driver for the virtio-rng device on the qemu platform. The
> >> device uses pci as a transport medium. The driver can be enabled with
> >> the following configs
> >>
> >> CONFIG_VIRTIO
> >> CONFIG_DM_RNG
> >> CONFIG_VIRTIO_PCI
> >> CONFIG_VIRTIO_RNG
> >>
> >> Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> >> ---
> >>   drivers/virtio/Kconfig         |  6 ++++
> >>   drivers/virtio/Makefile        |  1 +
> >>   drivers/virtio/virtio-uclass.c |  1 +
> >>   drivers/virtio/virtio_rng.c    | 72
> >> ++++++++++++++++++++++++++++++++++++++++++
> >>   include/virtio.h               |  4 ++-
> >>   5 files changed, 83 insertions(+), 1 deletion(-)
> >>   create mode 100644 drivers/virtio/virtio_rng.c
> >>
> >> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> >> index a9d5fd0..2e3dd3b 100644
> >> --- a/drivers/virtio/Kconfig
> >> +++ b/drivers/virtio/Kconfig
> >> @@ -59,4 +59,10 @@ config VIRTIO_BLK
> >>         This is the virtual block driver for virtio. It can be used with
> >>         QEMU based targets.
> >>
> >> +config VIRTIO_RNG
> >> +       bool "virtio rng driver"
> >> +       depends on VIRTIO
> >> +       help
> >> +         This is the virtual random number generator driver. It can
> >> be used
> >> +     with Qemu based targets.
> >>   endmenu
> >> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> >> index 4579044..dc88809 100644
> >> --- a/drivers/virtio/Makefile
> >> +++ b/drivers/virtio/Makefile
> >> @@ -9,3 +9,4 @@ obj-$(CONFIG_VIRTIO_PCI) += virtio_pci_legacy.o
> >> virtio_pci_modern.o
> >>   obj-$(CONFIG_VIRTIO_SANDBOX) += virtio_sandbox.o
> >>   obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
> >>   obj-$(CONFIG_VIRTIO_BLK) += virtio_blk.o
> >> +obj-$(CONFIG_VIRTIO_RNG) += virtio_rng.o
> >> diff --git a/drivers/virtio/virtio-uclass.c
> >> b/drivers/virtio/virtio-uclass.c
> >> index 34397d7..436faa4 100644
> >> --- a/drivers/virtio/virtio-uclass.c
> >> +++ b/drivers/virtio/virtio-uclass.c
> >> @@ -24,6 +24,7 @@
> >>   static const char *const virtio_drv_name[VIRTIO_ID_MAX_NUM] = {
> >>       [VIRTIO_ID_NET]        = VIRTIO_NET_DRV_NAME,
> >>       [VIRTIO_ID_BLOCK]    = VIRTIO_BLK_DRV_NAME,
> >> +    [VIRTIO_ID_RNG]        = VIRTIO_RNG_DRV_NAME,
> >>   };
> >>
> >>   int virtio_get_config(struct udevice *vdev, unsigned int offset,
> >> diff --git a/drivers/virtio/virtio_rng.c b/drivers/virtio/virtio_rng.c
> >> new file mode 100644
> >> index 0000000..19a0cc1
> >> --- /dev/null
> >> +++ b/drivers/virtio/virtio_rng.c
> >> @@ -0,0 +1,72 @@
> >> +// SPDX-License-Identifier: GPL-2.0+
> >> +/*
> >> + * Copyright (c) 2019, Linaro Limited
> >> + */
> >> +
> >> +#include <common.h>
> >> +#include <dm.h>
> >> +#include <rng.h>
> >> +#include <virtio_types.h>
> >> +#include <virtio.h>
> >> +#include <virtio_ring.h>
> >> +
> >> +struct virtio_rng_priv {
> >> +    struct virtqueue *rng_vq;
> >> +};
> >> +
> >> +static int virtio_rng_read(struct udevice *dev, void *data, size_t len)
> >> +{
> >> +    struct virtio_sg sg = { data, len };
> >> +    struct virtio_sg *sgs[] = { &sg };
> >> +    struct virtio_rng_priv *priv = dev_get_priv(dev);
> >> +    unsigned int rsize;
> >> +    int ret;
> >> +
> >> +    ret = virtqueue_add(priv->rng_vq, sgs, 0, 1);
> >> +    if (ret)
> >
> > Please, add a debug statement for each error path, e.g.
> >
> >          debug("%s: virtqueue_add() failed\n", __func__)
> >
> >> +        return ret;
> >> +
> >> +    virtqueue_kick(priv->rng_vq);
> >> +
> >> +    while (!virtqueue_get_buf(priv->rng_vq, &rsize))
> >> +        ;
> >> +
> >> +    return rsize;
> >
> > The return value is inconsistent with sandbox_rng_read() and
> > stm32_rng_read(). Both return 0 on success.
> >
> > With "return 0;" the driver works fine.
>
> I retested with
> -device virtio-rng-pci,disable-legacy=on,max-bytes=16,period=1000
>
> In this case virtqueue_get_buf() only returns a maximum of 16 bytes. All
> other bytes of data remain unchanged. If the next call occurs within
> 1000 milli-seconds virtqueue_get_buf() blocks until the period is over.
>
> So either you have to change the definition of the return parameter in
> patch 1/8 (and change the other drivers accordingly) or you have to add
> a loop to this driver that loops until len random bytes have been
> retrieved.
>
> I would prefer to add a loop in the driver instead of adding a loop in
> every consumer.
>

So I tried putting a loop in the virtio rng driver, but that does not work.
I was able to get it working with the loop in the consumer function. So I
have changed the return value of the read function in all the drivers to
return the number of bytes read, instead of returning 0. I think you will
have to change your logic in the rng command patch that you had sent.

-sughosh
diff mbox series

Patch

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index a9d5fd0..2e3dd3b 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -59,4 +59,10 @@  config VIRTIO_BLK
 	  This is the virtual block driver for virtio. It can be used with
 	  QEMU based targets.
 
+config VIRTIO_RNG
+       bool "virtio rng driver"
+       depends on VIRTIO
+       help
+         This is the virtual random number generator driver. It can be used
+	 with Qemu based targets.
 endmenu
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 4579044..dc88809 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -9,3 +9,4 @@  obj-$(CONFIG_VIRTIO_PCI) += virtio_pci_legacy.o virtio_pci_modern.o
 obj-$(CONFIG_VIRTIO_SANDBOX) += virtio_sandbox.o
 obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
 obj-$(CONFIG_VIRTIO_BLK) += virtio_blk.o
+obj-$(CONFIG_VIRTIO_RNG) += virtio_rng.o
diff --git a/drivers/virtio/virtio-uclass.c b/drivers/virtio/virtio-uclass.c
index 34397d7..436faa4 100644
--- a/drivers/virtio/virtio-uclass.c
+++ b/drivers/virtio/virtio-uclass.c
@@ -24,6 +24,7 @@ 
 static const char *const virtio_drv_name[VIRTIO_ID_MAX_NUM] = {
 	[VIRTIO_ID_NET]		= VIRTIO_NET_DRV_NAME,
 	[VIRTIO_ID_BLOCK]	= VIRTIO_BLK_DRV_NAME,
+	[VIRTIO_ID_RNG]		= VIRTIO_RNG_DRV_NAME,
 };
 
 int virtio_get_config(struct udevice *vdev, unsigned int offset,
diff --git a/drivers/virtio/virtio_rng.c b/drivers/virtio/virtio_rng.c
new file mode 100644
index 0000000..19a0cc1
--- /dev/null
+++ b/drivers/virtio/virtio_rng.c
@@ -0,0 +1,72 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2019, Linaro Limited
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <rng.h>
+#include <virtio_types.h>
+#include <virtio.h>
+#include <virtio_ring.h>
+
+struct virtio_rng_priv {
+	struct virtqueue *rng_vq;
+};
+
+static int virtio_rng_read(struct udevice *dev, void *data, size_t len)
+{
+	struct virtio_sg sg = { data, len };
+	struct virtio_sg *sgs[] = { &sg };
+	struct virtio_rng_priv *priv = dev_get_priv(dev);
+	unsigned int rsize;
+	int ret;
+
+	ret = virtqueue_add(priv->rng_vq, sgs, 0, 1);
+	if (ret)
+		return ret;
+
+	virtqueue_kick(priv->rng_vq);
+
+	while (!virtqueue_get_buf(priv->rng_vq, &rsize))
+		;
+
+	return rsize;
+}
+
+static int virtio_rng_bind(struct udevice *dev)
+{
+	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(dev->parent);
+
+	/* Indicate what driver features we support */
+	virtio_driver_features_init(uc_priv, NULL, 0, NULL, 0);
+
+	return 0;
+}
+
+static int virtio_rng_probe(struct udevice *dev)
+{
+	struct virtio_rng_priv *priv = dev_get_priv(dev);
+	int ret;
+
+	ret = virtio_find_vqs(dev, 1, &priv->rng_vq);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static const struct dm_rng_ops virtio_rng_ops = {
+	.read	= virtio_rng_read,
+};
+
+U_BOOT_DRIVER(virtio_rng) = {
+	.name	= VIRTIO_RNG_DRV_NAME,
+	.id	= UCLASS_RNG,
+	.bind	= virtio_rng_bind,
+	.probe	= virtio_rng_probe,
+	.remove = virtio_reset,
+	.ops	= &virtio_rng_ops,
+	.priv_auto_alloc_size = sizeof(struct virtio_rng_priv),
+	.flags	= DM_FLAG_ACTIVE_DMA,
+};
diff --git a/include/virtio.h b/include/virtio.h
index 654fdf1..561dcc3 100644
--- a/include/virtio.h
+++ b/include/virtio.h
@@ -22,10 +22,12 @@ 
 
 #define VIRTIO_ID_NET		1 /* virtio net */
 #define VIRTIO_ID_BLOCK		2 /* virtio block */
-#define VIRTIO_ID_MAX_NUM	3
+#define VIRTIO_ID_RNG		4 /* virtio rng */
+#define VIRTIO_ID_MAX_NUM	5
 
 #define VIRTIO_NET_DRV_NAME	"virtio-net"
 #define VIRTIO_BLK_DRV_NAME	"virtio-blk"
+#define VIRTIO_RNG_DRV_NAME	"virtio-rng"
 
 /* Status byte for guest to report progress, and synchronize features */