linux-kernel - Re: [PATCH] ARM: tegra: add basic SecureOS support

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Message-ID: <CAAVeFu+UMZikdWO20c9chvBcieOAUgOhz-nTEUpevFWnPNC_ZA@mail.gmail.com>
Date:	Mon, 10 Jun 2013 17:11:15 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Joseph Lo <josephl@...dia.com>,
	Karan Jhavar <kjhavar@...dia.com>,
	Varun Wadekar <vwadekar@...dia.com>,
	Chris Johnson <CJohnson@...dia.com>,
	Matthew Longnecker <MLongnecker@...dia.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: tegra: add basic SecureOS support

On Sat, Jun 8, 2013 at 1:33 AM, Stephen Warren <swarren@...dotorg.org> wrote:
>>> I think we need to separate the concept of support for *a* secure
>>> monitor, from support for a *particular* secure monitor.
>>
>> Agreed. In this case, can we assume that support for a specific secure
>> monitor is not arch-specific, and that this patch should be moved
>> outside of arch-tegra and down to arch/arm? In other words, the ABI of
>> a particular secure monitor should be the same no matter the chip,
>> shouldn't it?
>
> I would like to believe that the Trusted Foundations monitor had the
> same ABI irrespective of which Soc it was running on. However, I have
> absolutely no idea at all if that's true. Even if there's some common
> subset of the ABI that is identical across all SoCs, I wouldn't be too
> surprised if there were custom extensions for each different SoC, or
> just perhaps even each product.
>
> Can you research this and find out the answer?

Will do. Information about TF is scarce unfortunately.

> What we can always do is make a compatible property that lists
> everything[1], and have the driver match on the most specific value for
> now, but relax the driver's matching later if it turns out that the ABI
> is indeed common.
>
> [1] That'd need to be at least secure OS name, and secure OS version.
> Perhaps the SoC and board data can be deduced from the DT's top-level
> compatible properties; nvidia,tegra114-shield, nvidia,tegra114?

They can probably, but in theory nothing prevents a board from coming
with different secure monitors (or none at all). In this case, just
having the board name might not be enough.

Having a proper node for the firmware like David and Tomasz suggested
seems to be the best way to make sure we cover all cases - I think I
will try to do it this way for the next version, and hopefully come
with a binding that is useful for everyone.

Thanks,
Alex.
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