[PATCH v2 1/2] lib: uuid: use RNG device if present

[Torsten Duwe <duwe@lst.de>]

On Fri, 18 Dec 2020 19:29:12 -0700
Simon Glass <sjg@chromium.org> wrote:

> > -       int i;
> > -
> > -       srand(get_ticks() + rand());
> > +       int i, ret;
> > +       struct udevice *devp;
> > +       u8 randv = 0;
> > +
> > +#if defined(CONFIG_DM_RNG)
> 
> This seems a little backwards to me. The caller should request a RNG
> device, getting either a hardware one or a software one, and then call
> the uclass method to get the uuid.

Strictly speaking, there's no such thing as a "software RNG". The term
"DRBG" was coined for accurateness, "deterministic random bit
generator". The oxymoron "deterministic random" pretty much nails it.
Alternatively, it can be called "pseudo" RNG.
rand() and srand() exactly implement such a mechanism already, with low
coding overhead. U-Boot runs fine with them most of the time, but there
are rare cases where real entropy would be needed. This is what these
two patches are about. In case there's more, I already speculated about
a centralised entity in my response to the v1 cover letter, but for now
these two changes should do.

> > +       ret = uclass_get_device(UCLASS_RNG, 0, &devp);
> > +       if (ret) {
> > +               ret = dm_rng_read(devp, &randv, sizeof(randv));
> > +               if (ret < 0)
> > +                       randv = 0;
> > +       }
> > +       if (randv)
> > +               srand(randv);
> > +       else
> > +#endif
> > +               srand(get_ticks() + rand());
> >
> >         /* Set all fields randomly */
> >         for (i = 0; i < 4; i++)
[ rand() usage following here ^ ]

The #ifdefs are already gone in v3.

	Torsten