linux-kernel - Re: [PATCH v6 1/5] ARM: add basic support for Trusted Foundations

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Date:	Mon, 16 Sep 2013 10:50:38 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Alexandre Courbot <acourbot@...dia.com>
CC:	Russell King <linux@....linux.org.uk>,
	Tomasz Figa <t.figa@...sung.com>,
	Dave Martin <Dave.Martin@....com>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Kevin Hilman <khilman@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>, gnurou@...il.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 1/5] ARM: add basic support for Trusted Foundations

On 09/15/2013 03:40 AM, Alexandre Courbot wrote:
> Trusted Foundations is a TrustZone-based secure monitor for ARM that
> can be invoked using the same 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.
> 
> Note: The API followed by Trusted Foundations does *not* follow the SMC
> calling conventions. It has nothing to do with PSCI neither and is only
> relevant to devices that use Trusted Foundations (like most Tegra-based
> retail devices).

> diff --git a/arch/arm/firmware/trusted_foundations.c b/arch/arm/firmware/trusted_foundations.c

> +#if IS_ENABLED(CONFIG_OF)
> +void of_register_trusted_foundations(void)
> +{
> +	struct device_node *node;
> +	struct trusted_foundations_platform_data pdata;
> +	int err;
> +
> +	node = of_find_compatible_node(NULL, NULL, "tl,trusted-foundations");
> +	if (!node)
> +		return;
...

> diff --git a/arch/arm/include/asm/trusted_foundations.h b/arch/arm/include/asm/trusted_foundations.h

> +#if IS_ENABLED(CONFIG_TRUSTED_FOUNDATIONS)
> +void register_trusted_foundations(struct trusted_foundations_platform_data *pd);
> +#if IS_ENABLED(CONFIG_OF)
> +void of_register_trusted_foundations(void);
> +#endif

I still don't think that's correct.

If TF support is enabled, yet DT support is not enabled, then there is
no prototype, implementation, or dummy implementation for
of_register_trusted_foundations(). I think there should be a dummy
implementation in this case, shouldn't there?

> +
> +#else /* CONFIG_TRUSTED_FOUNDATIONS */
> +
> +#include <linux/printk.h>
> +#include <linux/of.h>
> +#include <asm/bug.h>
> +
> +static inline void register_trusted_foundations(
> +				   struct trusted_foundations_platform_data *pd)
> +{
> +	panic("No support for Trusted Foundations, stopping...\n");
> +}
> +
> +#if IS_ENABLED(CONFIG_OF)
> +static inline void of_register_trusted_foundations(void)
> +{
> +	/* If we find the target should enable TF but does not support it,
> +	 * fail as the system won't be able to do much anyway */
> +	if (of_find_compatible_node(NULL, NULL, "tl,trusted-foundations"))
> +		register_trusted_foundations(NULL);
> +}
> +#else
> +static inline void of_register_trusted_foundations(void)
> +{
> +}
> +#endif /* CONFIG_OF */

That's more complex than it needs to be; there is a dummy
of_find_compatible_node() in the !OF case, so you don't need to ifdef
the implementation of of_register_trusted_foundations(); you just need
the first implementation here.

> +#endif /* CONFIG_TRUSTED_FOUNDATIONS */

In summary, I think you need:

If TF is enabled, always implement of_register_trusted_foundations() in
the C file, and rely on of_find_compatible_node() to return NULL if
!CONFIG_OF.

If TF is not enabled, implement the inline version in the header file,
and again rely on of_find_compatible_node() to return NULL if !CONFIG_OF.

Unless I'm missing something!
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