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

[Sughosh Ganu]

On Wed, 25 Dec 2019 at 07:00, Heinrich Schuchardt <xypron.glpk at 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 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.
>

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