linux-kernel - Re: [PATCH v2 03/11] m68k: use ktime_read_raw_clock() for random_get

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Date:   Tue, 12 Apr 2022 00:07:58 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, "Theodore Ts'o" <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "David S . Miller" <davem@...emloft.net>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        sparclinux@...r.kernel.org, linux-um@...ts.infradead.org,
        X86 ML <x86@...nel.org>, linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v2 03/11] m68k: use ktime_read_raw_clock() for
 random_get_entropy() instead of zero

Hi Thomas,

On Mon, Apr 11, 2022 at 10:18 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> > diff --git a/arch/m68k/include/asm/timex.h b/arch/m68k/include/asm/timex.h
> > index 6a21d9358280..5351b10e1b18 100644
> > --- a/arch/m68k/include/asm/timex.h
> > +++ b/arch/m68k/include/asm/timex.h
> > @@ -35,7 +35,7 @@ static inline unsigned long random_get_entropy(void)
> >  {
> >       if (mach_random_get_entropy)
> >               return mach_random_get_entropy();
> > -     return 0;
> > +     return ktime_read_raw_clock();
>
> I'd rather do something like this in a common header:
>
> unsigned long random_get_entropy_fallback(void);
>
> and use random_get_entropy_fallback() in the architecture specific
> files.
>
> That way you can encapsulate the fallback implementation in the random
> code and if it turns out that ktime_read_raw_clock() is a stupid idea or
> someone has a better idea then you have to change exactly one place and
> not patch the whole tree again.

Absolutely. That's a good idea. I'll do that for v3.

Jason