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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
        x86@kernel.org
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Will Deacon <will@kernel.org>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Borislav Petkov <bp@suse.de>,
        Heiko Carstens <hca@linux.ibm.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Harald Freudenberger <freude@linux.ibm.com>
Subject: Re: [PATCH v2] random: handle archrandom in plural words
In-Reply-To: <20220717200356.75060-1-Jason@zx2c4.com>
References: <YtP1+MJ1tNdJA60l@zx2c4.com>
 <20220717200356.75060-1-Jason@zx2c4.com>
Date:   Mon, 18 Jul 2022 16:31:11 +1000
Message-ID: <87a697dj9s.fsf@mpe.ellerman.id.au>
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"Jason A. Donenfeld" <Jason@zx2c4.com> writes:
> The archrandom interface was originally designed for x86, which supplies
> RDRAND/RDSEED for receiving random words into registers, resulting in
> one function to generate an int and another to generate a long. However,
> other architectures don't follow this.
>
> On arm64, the SMCCC TRNG interface can return between 1 and 3 words. On
> s390, the CPACF TRNG interface can return between 1 and 32 words for the
> same cost as for one word. On UML, the os_getrandom() interface can return
> arbitrary amounts.
>
> So change the api signature to take a "words" parameter designating the
> maximum number of words requested, and then return the number of words
> generated.

On powerpc a word is 32-bits and a doubleword is 64-bits (at least
according to the ISA). I think that's also true on other 64-bit
architectures.

You could avoid any confusion by defining the API in terms of "longs"
rather than "words".

But that's just a comment, see what others think.

>  arch/powerpc/include/asm/archrandom.h |  30 ++------
>  arch/powerpc/kvm/book3s_hv.c          |   2 +-

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers