[PATCH v3 5/8] sandbox: rng: Add a random number generator(rng) driver

Sughosh Ganu
2019-12-16T18:59:15Z

hi Patrick,

On Mon, 16 Dec 2019 at 18:00, Patrick DELAUNAY <patrick.delaunay@st.com>
wrote:

> Hi,
>
> > From: U-Boot <u-boot-bounces@lists.denx.de> On Behalf Of Sughosh Ganu
> > Sent: vendredi 13 dÃ©cembre 2019 08:14
> >
> > Add a sandbox driver for random number generation. Mostly aimed at
> providing a
> > unit test for rng uclass.
> >
> > Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> > Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
> > ---
> > arch/sandbox/dts/test.dts | 4 ++++
> > drivers/rng/Kconfig | 7 +++++++
> > drivers/rng/Makefile | 1 +
> > drivers/rng/sandbox_rng.c | 36 ++++++++++++++++++++++++++++++++++++
> > 4 files changed, 48 insertions(+)
> > create mode 100644 drivers/rng/sandbox_rng.c
>

<snip>

>
> > a/drivers/rng/sandbox_rng.c b/drivers/rng/sandbox_rng.c new file mode
> 100644
> > index 0000000..c5be552
> > --- /dev/null
> > +++ b/drivers/rng/sandbox_rng.c
> > @@ -0,0 +1,36 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (c) 2019, Linaro Limited
> > + */
> > +
> > +#include <common.h>
> > +#include <dm.h>
> > +#include <rng.h>
> > +
> > +static unsigned long random = 0xdeadbeef;
> > +
> > +static int sandbox_rng_read(struct udevice *dev, void *data, size_t
> > +len) {
>
> Add protection on length I think:
> If (len != sizeof(random))
> retrun - EINVAL;
>

Ok. Will add this check.

>
> or treat the case len > 4 with loop ?
>
> > + random ^= ~0UL;
> > + *(unsigned long *)data = random;
> > +
> > + return sizeof(random);
>
> Read is OK, so I think the correct return value is 0:
>

Ok. Will change.

>
> return 0;
>
> NB: result (int) can be not enough to return the value read (size_t)
>
> PS: it not really a random generator here but simple sequence
> 0xdeadbeef -> 0x21524110 -> 0xdeadbeef
>
> It is enough for unitary test, but is is enough for sandbox ?
> we could reused PRNG code from lib/rand.c ?
>

I actually wrote this solely from the point of view of adding a unit test
for the rng uclass. For which i think the simple sequence above should
suffice. Do you have a strong opinion on this. If so, i can change the
logic.

-sughosh

>
>