linux-kernel - [PATCH v2 2/6] ARM: trusted_foundations: fallback when TF support is missing

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Date:	Fri, 7 Feb 2014 13:35:02 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Tomasz Figa <t.figa@...sung.com>
CC:	Olof Johansson <olof@...om.net>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<gnurou@...il.com>, Alexandre Courbot <acourbot@...dia.com>
Subject: [PATCH v2 2/6] ARM: trusted_foundations: fallback when TF support is missing

When Trusted Foundations is detected as present on the system, but
Trusted Foundations support is not built into the kernel, the kernel
used to issue a panic very early during boot, leaving little clue to the
user as to what is going wrong.

It turns out that even without TF support built-in, the kernel can boot
on a TF-enabled system provided that SMP and cpuidle are disabled. This
patch does this and continue booting on one CPU, leaving the user with a
usable (however degraded) system.

Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
 arch/arm/include/asm/trusted_foundations.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/trusted_foundations.h b/arch/arm/include/asm/trusted_foundations.h
index 997862fd5d77..b5f7705abcb0 100644
--- a/arch/arm/include/asm/trusted_foundations.h
+++ b/arch/arm/include/asm/trusted_foundations.h
@@ -30,6 +30,8 @@
 #include <linux/printk.h>
 #include <linux/bug.h>
 #include <linux/of.h>
+#include <linux/cpu.h>
+#include <linux/smp.h>
 
 struct trusted_foundations_platform_data {
 	unsigned int version_major;
@@ -47,10 +49,13 @@ static inline void register_trusted_foundations(
 				   struct trusted_foundations_platform_data *pd)
 {
 	/*
-	 * If we try to register TF, this means the system needs it to continue.
-	 * Its absence if thus a fatal error.
+	 * If the system requires TF and we cannot provide it, continue booting
+	 * but disable features that cannot be provided.
 	 */
-	panic("No support for Trusted Foundations, stopping...\n");
+	pr_err("No support for Trusted Foundations, continuing in degraded mode.\n");
+	pr_err("Secondary processors as well as CPU PM will be disabled.\n");
+	setup_max_cpus = 0;
+	cpu_idle_poll_ctrl(true);
 }
 
 static inline void of_register_trusted_foundations(void)
-- 
1.8.5.3

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