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Date:   Fri, 5 Jun 2020 09:09:06 +0100
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Neal Liu <neal.liu@mediatek.com>
Cc:     Marc Zyngier <maz@kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Julius Werner <jwerner@google.com>,
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        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        Rob Herring <robh+dt@kernel.org>,
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        Matthias Brugger <matthias.bgg@gmail.com>,
        Crystal Guo =?utf-8?B?KOmDreaZtik=?= <Crystal.Guo@mediatek.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Security Random Number Generator support
Message-ID: <20200605080905.GF1551@shell.armlinux.org.uk>
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On Fri, Jun 05, 2020 at 03:19:03PM +0800, Neal Liu wrote:
> On Wed, 2020-06-03 at 17:34 +0800, Russell King - ARM Linux admin wrote:
> > This kind of thing is something that ARM have seems to shy away from
> > doing - it's a point I brought up many years ago when the whole
> > trustzone thing first appeared with its SMC call.  Those around the
> > conference table were not interested - ARM seemed to prefer every
> > vendor to do off and do their own thing with the SMC interface.
> 
> Does that mean it make sense to model a sec-rng driver, and get each
> vendor's SMC function id by DT node?

_If_ vendors have already gone off and decided to use different SMC
function IDs for this, while keeping the rest of the SMC interface
the same, then the choice has already been made.

I know on 32-bit that some of the secure world implementations can't
be changed; they're burnt into the ROM. I believe on 64-bit that isn't
the case, which makes it easier to standardise.

Do you have visibility of how this SMC is implemented in the secure
side?  Is it in ATF, and is it done as a vendor hack or is there an
element of generic implementation to it?  Has it been submitted
upstream to the main ATF repository?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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