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

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Date:   Sun, 24 Apr 2022 11:51:38 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
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        Dominik Brodowski <linux@...inikbrodowski.net>,
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        Catalin Marinas <catalin.marinas@....com>,
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        Geert Uytterhoeven <geert@...ux-m68k.org>,
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Subject: Re: [PATCH v4 04/11] mips: use fallback for random_get_entropy()
 instead of zero

On Sun, 24 Apr 2022, Jason A. Donenfeld wrote:

> > unconditionally.  I think this discovery asks for code optimisation, which 
> > I'll try to cook up sometime.
> 
> At some point too, by the way, we might also consider putting that into
> a .c file rather than a static inline in the .h, since that function is
> starting to get sort of big.

 This code is supposed to produce one to a couple of machine instructions 
for the majority of configurations.  This is because the conditionals used 
are usually compile-time constants.  Therefore I think it will be good to 
continue having it as `static inline' functions.  Cf. the analysis in 
commit 06947aaaf9bf ("MIPS: Implement random_get_entropy with CP0 
Random").

 If this code does expand to a longer sequence for some platforms, then 
either they need to be verified whether they can be optimised (just as I 
note here for the DEC systems) or we can consider making these functions 
`extern inline' instead, with out-of-line code available from a .a file in 
case the compiler decides the code is too large for inlining to be worth 
doing after all.  Though I don't expect the latter case to be required 
really.

  Maciej