Hi all,
I am in the process of adding a device-tree binding for OMAP timers and
I have encountered a scenario where ideally it would be useful to remove
a device-tree node at runtime.
The scenario is this ...
1. OMAP3 devices may or may not have security features enabled. Security
enabled devices are known as high-secure (HS) and devices without
security are known as general purpose (GP).
2. For OMAP3 devices there are 12 general purpose timers available.
3. On secure devices the 12th timer is reserved for secure usage and so
cannot be used by the kernel, where as for a GP device it is available.
4. We can detect the OMAP device type, secure or GP, at runtime via an
on-chip register.
5. Today, when not using DT, we do not register the 12th timer as a linux
device if the device is secure.
When migrating the timers to DT, I need a way to prevent this 12th timer
from being registered as a device on a secure device. The options I have
considered are ...
a. Have separate a omap3.dtsi for GP and secure devices or place the
node for the 12th timer in a omap3-gp.dtsi that is only used for
boards with GP devices. The downside of this is that for boards
that can support GP and secure device (such as the omap3 SDP) we
require a separate dtb blob.
b. Remove the timer node dynamically at runtime using the
of_node_detach() API. In this solution we define a "ti,timer-secure"
property that the 12th timer on omap3 devices would have and at
runtime if we are a secure omap3 device, we search the timer nodes
for any nodes with this property and remove them.
Option B, seems to be the better option but requires me to enable
CONFIG_OF_DYNAMIC for all omap devices and I was not sure if there is any
downside to doing so. Enabling this feature does not seem to add much code
as far as I can tell, however, I wanted to get some feedback before
proposing this. Also if there are any other options I should consider then
please let me know.
For option B, the timer node would look like ...
+ timer12: timer@48304000 {
+ compatible = "ti,omap3-timer";
+ ti,hwmods = "timer12";
+ ti,timer-alwon;
+ ti,timer-secure;
+ };
I would then add the following function to the omap timer code to search
for any timers with the "ti,timer-secure" on a secure device and enable
the OF_DYNAMIC option. Right now it is only timer 12 on OMAP3 that
requires this, but I have made the function generic so that it could
handle other devices (but none exist today that I am aware of).
diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
index 8c22a8e..5e38946 100644
--- a/arch/arm/mach-omap2/timer.c
+++ b/arch/arm/mach-omap2/timer.c
@@ -36,6 +36,7 @@
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/slab.h>
+#include <linux/of.h>
#include <asm/mach/time.h>
#include <plat/dmtimer.h>
@@ -482,6 +483,35 @@ static int __init omap2_dm_timer_init(void)
}
arch_initcall(omap2_dm_timer_init);
+static struct of_device_id omap3_timer_match[] __initdata = {
+ { .compatible = "ti,omap3-timer", },
+ { }
+};
+
+/**
+ * omap_dmtimer_init - initialisation function when device tree is used
+ *
+ * For secure OMAP3 devices, timers with property "ti,timer-secure" cannot
+ * be used by the kernel as they are reserved. Therefore, to prevent the
+ * kernel registering these devices remove them dynamically from the device
+ * tree on boot.
+ */
+void __init omap_dmtimer_init(void)
+{
+ struct device_node *np;
+
+ if (!cpu_is_omap34xx())
+ return;
+
+ /* If we are a secure device, remove any secure timer nodes */
+ if ((omap_type() == OMAP2_DEVICE_TYPE_GP)) {
+ for_each_matching_node(np, omap3_timer_match) {
+ if (of_get_property(np, "ti,timer-secure", NULL))
+ of_detach_node(np);
+ }
+ }
+}
+
/**
* omap2_override_clocksource - clocksource override with user configuration
*
diff --git a/arch/arm/plat-omap/Kconfig b/arch/arm/plat-omap/Kconfig
index ad95c7a..d2daee0 100644
--- a/arch/arm/plat-omap/Kconfig
+++ b/arch/arm/plat-omap/Kconfig
@@ -27,6 +27,7 @@ config ARCH_OMAP2PLUS
select GENERIC_IRQ_CHIP
select OMAP_DM_TIMER
select USE_OF
+ select OF_DYNAMIC
select PROC_DEVICETREE if PROC_FS
help
"Systems based on OMAP2, OMAP3 or OMAP4"
If you prefer I send out my complete series (I believe it is only 3 patches)
for adding the timers I can do that too.
Cheers
Jon
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