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

[Heinrich Schuchardt]

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 at 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 */
>>
>>
>
>