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

From: Florian Fainelli <f.fainelli@gmail.com>
To: Marc Zyngier <maz@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	pawel.moll@arm.com
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	DTML <devicetree@vger.kernel.org>,
	"Herbert Xu" <herbert@gondor.apana.org.au>,
	wsd_upstream <wsd_upstream@mediatek.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Sean Wang" <sean.wang@kernel.org>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Neal Liu" <neal.liu@mediatek.com>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"Matt Mackall" <mpm@selenic.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Crystal Guo (郭晶)" <Crystal.Guo@mediatek.com>,
	"Will Deacon" <will@kernel.org>, "Lars Persson" <lists@bofh.nu>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 3/3] hwrng: add mtk-sec-rng driver
Date: Mon, 2 Dec 2019 20:16:37 -0800	[thread overview]
Message-ID: <299029b0-0689-c2c4-4656-36ced31ed513@gmail.com> (raw)
In-Reply-To: <20191202191146.79e6368c@why>


On 12/2/2019 11:11 AM, Marc Zyngier wrote:
> On Mon, 2 Dec 2019 16:12:09 +0000
> Ard Biesheuvel <ard.biesheuvel@linaro.org> 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.
> 
> Absolutely. I'd love to see a standard, ARM-specified, virtualizable
> RNG that is abstracted from the HW.

Do you think we could use virtio-rng on top of a modified virtio-mmio
which instead of being backed by a hardware mailbox, could use hvc/smc
calls to signal writes to shared memory and get notifications via an
interrupt? This would also open up the doors to other virtio uses cases
beyond just RNG (e.g.: console, block devices?). If this is completely
stupid, then please disregard this comment.
-- 
Florian