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Date:   Thu, 12 Dec 2019 14:43:55 +0000
From:   Sudeep Holla <sudeep.holla@arm.com>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     Neal Liu <neal.liu@mediatek.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        Lars Persson <lists@bofh.nu>,
        Mark Rutland <mark.rutland@arm.com>,
        DTML <devicetree@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        wsd_upstream <wsd_upstream@mediatek.com>,
        Sean Wang <sean.wang@kernel.org>,
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        Matt Mackall <mpm@selenic.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
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Subject: Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver
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On Mon, Dec 02, 2019 at 04:12:09PM +0000, Ard Biesheuvel wrote:
> (adding some more arm64 folks)
> 
> On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@mediatek.com> wrote:
> >
> > On Fri, 2019-11-29 at 18:02 +0800, Lars Persson wrote:
> > > Hi Neal,
> > >
> > > On Wed, Nov 27, 2019 at 3:23 PM Neal Liu <neal.liu@mediatek.com> wrote:
> > > >
> > > > For MediaTek SoCs on ARMv8 with TrustZone enabled, peripherals like
> > > > entropy sources is not accessible from normal world (linux) and
> > > > rather accessible from secure world (ATF/TEE) only. This driver aims
> > > > to provide a generic interface to ATF rng service.
> > > >
> > >
> > > I am working on several SoCs that also will need this kind of driver
> > > to get entropy from Arm trusted firmware.
> > > If you intend to make this a generic interface, please clean up the
> > > references to MediaTek and give it a more generic name. For example
> > > "Arm Trusted Firmware random number driver".
> > >
> > > It will also be helpful if the SMC call number is configurable.
> > >
> > > - Lars
> >
> > Yes, I'm trying to make this to a generic interface. I'll try to make
> > HW/platform related dependency to be configurable and let it more
> > generic.
> > Thanks for your suggestion.
> >
> 
> I don't think it makes sense for each arm64 platform to expose an
> entropy source via SMC calls in a slightly different way, and model it
> as a h/w driver. Instead, we should try to standardize this, and
> perhaps expose it via the architectural helpers that already exist
> (get_random_seed_long() and friends), so they get plugged into the
> kernel random pool driver directly.
> 
> Note that in addition to drivers based on vendor SMC calls, we already
> have a RNG h/w driver based on OP-TEE as well, where the driver
> attaches to a standardized trusted OS interface identified by a UUID,
> and which also gets invoked via SMC calls into secure firmware.

Yes, I agree. I had raised the issue internally and forgot to follow up.
I raised this few months back after I read a blog[1]

--
Regards,
Sudeep

[1] https://community.arm.com/developer/ip-products/processors/f/cortex-a-forum/43679/arm-really-should-standardize-an-smc-interface-for-hardware-random-number-generators