Linux timer interrupts not working when booting in normal-world

Linux timer interrupts not working when booting in normal-world

[Nuno Santos]

Hi

I'm currently playing with the TrustZone technology on the Tegra2 
Harmony board, and my goal is to boot Linux not in the secure world (as 
it is in mainstream Linux), but in the normal world. However, in doing 
this, timer interrupts are not being triggered and the system halts 
early in the bootstrap stage. I'd like to ask if anyone could give me a 
hint for why this is happening.

So far I managed to set up the secure world environment so that we can 
invoke secure services through the SMC instruction from the normal 
world. This configuration step is done by u-boot, after which it enters 
normal world and jumps to Linux. To make sure that Linux can handle 
interrupts freely, in this setup phase, I assign the SCR register 0x3 
(EA, FIQ, and IRQ bit are clear, and AW and FW are set).

Assuming that this configuration is correct, one possible explanation 
for the absence of timer interrupts is that the Harmony board may impose 
some restrictions to the timer re-configuration in the normal world. 
Does anyone have an idea if there are such restrictions? If not, is 
there any other explanation for this? Is there some configuration step 
that I'm missing?

Thank you very much in advance!
--Nuno Santos

Re: Linux timer interrupts not working when booting in normal-world

[Stephen Warren]

On 09/12/2012 08:01 AM, Nuno Santos wrote:
> Hi
> 
> I'm currently playing with the TrustZone technology on the Tegra2
> Harmony board, and my goal is to boot Linux not in the secure world (as
> it is in mainstream Linux), but in the normal world. However, in doing
> this, timer interrupts are not being triggered and the system halts
> early in the bootstrap stage. ...

This isn't a topic I really know anything about. I'd assume the answer
to your question is ARM-generic and not Tegra-specific; you may have
better luck asking on the main ARM Linux mailing list.

I assume you're using (or at least can reproduce the issue with)
mainline Linux, and not a downstream NVIDIA kernel? If you're using an
NVIDIA kernel, I'd suggest asking your contacts at NVIDIA about it.

> Assuming that this configuration is correct, one possible explanation
> for the absence of timer interrupts is that the Harmony board may impose
> some restrictions to the timer re-configuration in the normal world. ...

I don't think the board can impose any restrictions; the boot ROM in the
Tegra SoC is presumably identical across all instances of Tegra20, and
the code that runs after that is whatever bootloader you built and
flashed onto the board. Unless of course there are strapping/fuse
options that affect this, but if any do exist, and since Harmony is a
developer board, I'd imagine their settings would be left as wide open
as possible.

Sorry I'm not very helpful!

Re: Linux timer interrupts not working when booting in normal-world

[Antti P Miettinen]

Nuno Santos <nuno.m.santos-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
writes:
> I'm currently playing with the TrustZone technology on the Tegra2
> Harmony board, and my goal is to boot Linux not in the secure world
> (as it is in mainstream Linux), but in the normal world. However, in
> doing this, timer interrupts are not being triggered and the system
> halts early in the bootstrap stage. I'd like to ask if anyone could
> give me a hint for why this is happening.

GIC configuration? I'm not at all familiar with TZ, but you might need
to configure the interrupts as non-secure:

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ihi0048a/CHDCEAIF.html

So you have a secure monitor you can create SMCs for? Is that code
available?

--
Antti P Miettinen
http://www.iki.fi/~ananaza/