linux-kernel - Re: [PATCH 3/3] hwrng: ba431-rng: add support for BA431 hwrng

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Date:   Fri, 29 May 2020 11:12:31 -0600
From:   Rob Herring <robh@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Olivier Sobrie <olivier.sobrie@...exinsight.com>,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>, DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Waleed Ziad <waleed94ziad@...il.com>,
        sebastien.rabou@...exinsight.com
Subject: Re: [PATCH 3/3] hwrng: ba431-rng: add support for BA431 hwrng

On Mon, May 25, 2020 at 10:28:46PM +0200, Arnd Bergmann wrote:
> On Mon, May 25, 2020 at 10:07 PM Olivier Sobrie
> <olivier.sobrie@...exinsight.com> wrote:
> >
> > Silex insight BA431 is an IP designed to generate random numbers that
> > can be integrated in various FPGA.
> > This driver adds support for it through the hwrng interface.
> >
> > This driver is used in Silex Insight Viper OEM boards.
> >
> > Signed-off-by: Olivier Sobrie <olivier.sobrie@...exinsight.com>
> > Signed-off-by: Waleed Ziad <waleed94ziad@...il.com>
> 
> The driver looks good to me.
> 
> Acked-by: Arnd Bergmann  <arnd@...db.de>
> 
> >  drivers/char/hw_random/Kconfig     |  10 ++
> >  drivers/char/hw_random/Makefile    |   1 +
> >  drivers/char/hw_random/ba431-rng.c | 240 +++++++++++++++++++++++++++++
> 
> I wonder if we should move drivers/char/hw_random to its own top-level drivers
> subsystem outside of drivers/char. It seems to be growing steadily and is larger
> than a lot of other subsystems with currently 34 drivers in there.
> 
> Not your problem though.
> 
> > +       /* Wait until the state changed */
> > +       for (i = 0; i < BA431_RESET_READ_STATUS_RETRIES; ++i) {
> > +               state = ba431_trng_get_state(ba431);
> > +               if (state >= BA431_STATE_STARTUP)
> > +                       break;
> > +
> > +               udelay(BA431_RESET_READ_STATUS_INTERVAL);
> > +       }
> 
> Looking for something to improve, I noticed that this loop can take over
> a millisecond to time out, and it always runs in non-atomic context.
> It may be better to use usleep_range() than udelay().

Or better yet, use the register polling helpers.

Rob