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

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Message-ID: <20200529203321.GA793664@ultraoso.localdomain>
Date:   Fri, 29 May 2020 22:33:21 +0200
From:   Olivier Sobrie <olivier.sobrie@...exinsight.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, 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 Fri, May 29, 2020 at 11:12:31AM -0600, Rob Herring wrote:
> 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.

Indeed, thanks for the suggestion.
I'll replace this loop by the readx_poll_timeout() macro.

Olivier