linux-kernel - Re: [PATCH v4 04/11] mips: use fallback for random_get

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Message-ID: <alpine.DEB.2.21.2204131331450.9383@angie.orcam.me.uk>
Date:   Wed, 13 Apr 2022 13:46:29 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        tglx@...utronix.de, 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>,
        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@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-riscv@...ts.infradead.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, x86@...nel.org,
        linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v4 04/11] mips: use fallback for random_get_entropy()
 instead of zero

On Wed, 13 Apr 2022, Thomas Bogendoerfer wrote:

> > diff --git a/arch/mips/include/asm/timex.h b/arch/mips/include/asm/timex.h
> > index b05bb70a2e46..abc60a6395e3 100644
> > --- a/arch/mips/include/asm/timex.h
> > +++ b/arch/mips/include/asm/timex.h
> > @@ -94,7 +94,7 @@ static inline unsigned long random_get_entropy(void)
> >  	else if (likely(imp != PRID_IMP_R6000 && imp != PRID_IMP_R6000A))
> >  		return read_c0_random();
> >  	else
> > -		return 0;	/* no usable register */
> > +		return random_get_entropy_fallback();	/* no usable register */
> >  }
> >  #define random_get_entropy random_get_entropy
> >  
> > -- 
> > 2.35.1
> 
> Acked-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>

 Or we could drop the PRID_IMP_R6000/A check and the final `else' clause 
entirely, as we don't even pretend to support the R6k at all anymore, and 
this is the final reference remaining.  For one we no longer handle the 
CPU in `cpu_probe_legacy' so any attempt to boot on such a CPU would 
inevitably fail as no CPU options would be set (we probably should have a 
`panic' or suchlike as the default case for the switch statement there).

 Therefore I'm all for removing this piece instead, complementing commit 
3b2db173f012 ("MIPS: Remove unused R6000 support"), where it should have 
really happened.

  Maciej