linux-kernel - Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

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Date:   Mon, 2 Dec 2019 16:12:09 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Neal Liu <neal.liu@...iatek.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>
Cc:     Lars Persson <lists@...h.nu>, Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        Sean Wang <sean.wang@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Crystal Guo (郭晶) <Crystal.Guo@...iatek.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Matt Mackall <mpm@...enic.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver

(adding some more arm64 folks)

On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@...iatek.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@...iatek.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.