linux-kernel - Re: [PATCH v3 1/5] ARM: add basic Trusted Foundations support

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Message-ID: <520D500C.5070901@wwwdotorg.org>
Date:	Thu, 15 Aug 2013 16:02:52 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Dave Martin <Dave.Martin@....com>
CC:	Alexandre Courbot <acourbot@...dia.com>, gnurou@...il.com,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	devicetree@...r.kernel.org, Jassi Brar <jassisinghbrar@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	linux-kernel@...r.kernel.org, Joseph Lo <josephl@...dia.com>,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/5] ARM: add basic Trusted Foundations support

On 08/15/2013 05:52 AM, Dave Martin wrote:
> On Tue, Aug 13, 2013 at 11:29:48AM +0900, Alexandre Courbot wrote:
>> Trusted Foundations is a TrustZone-based secure monitor for ARM that
>> can be invoked  using a consistent smc-based API on all supported
>> platforms. This patch adds initial basic support for Trusted
>> Foundations using the ARM firmware API. Current features are limited
>> to the ability to boot secondary processors.

>> diff --git a/Documentation/devicetree/bindings/arm/firmware/tl,trusted-foundations.txt b/Documentation/devicetree/bindings/arm/firmware/tl,trusted-foundations.txt

>> +Required properties:
>> +- compatible : "tl,trusted-foundations"
>> +- version : Must contain the version number string of the Trusted Foundation
>> +	firmware.
> 
> Are you sure there is no low-level way to probe vendor and version info?
> If there is, then the DT should describe nothing except the fact that
> the probe interface exists.
> 
> I also worry that two integrations on different SoCs might have the
> same version number, yet still be different due to vendor-specific
> features and options.

I would expect HW-specific compatible values also to be present in a DT.
For example, perhaps:

compatible = "tl,trusted-foundations-nvidia-shield",
"tl,trusted-foundations";

(nvidia vendor, shield board/implementation)

This would allow matching on the specific value
"tl,trusted-foundations-nvidia-shield" in the future if some quirking
was needed, but if this wasn't needed, drivers could just bind to the
generic "tl,trusted-foundations".

>> +- version : Must contain the version number string of the Trusted Foundation
>> +	firmware.
> 
> Are you sure there is no low-level way to probe vendor and version info?
> If there is, then the DT should describe nothing except the fact that
> the probe interface exists.
> 
> I also worry that two integrations on different SoCs might have the
> same version number, yet still be different due to vendor-specific
> features and options.

Talking of the version - if we do need to represent this in the DT, how
about 2 separate cells for major/minor version rather than encoding it
into a string? Then, no parsing would be required.
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