DRA750: nonsecure callback/RPC from PPA secure FIQ handler

HI

can you clarify on the intended usage for FIQ, what peripheral is hooked up as FIQ and how do you intend to use this

Dont think we have an usage example for what you have outlined above, will check again once if you can share more details on the intended usage with PPA and how you want the notification to be dispatched and handled from Linux

Hi Sriram,

FIQ interrupts are generated by PMU, intended use is as poor man's NMI to detect hard lockup condition in kernel.

I have a Linux kernel patch (by Linaro, can provide details if requested) which sets up watchdig events by PMU, and uses FIQ as NMI replacement to detect lockup condition, and provide backtrace of the locked core.

Thus we have an interrupt (FIQ) handler in kernel which ais supposed to acknowledge the interrupt on PMU, and do kernel bookkeeping.

I get as far as registering the interrupt in PPA, and registering a FIQ handler (inside PPA). This handler is being called.

However, up to now I failed to call the kernel handler code from PPA FIQ callback.

Hope this explanation helps.

Regards,

Jürgen

Hi Jürgen,

So you are now trying to signal the non-secure side from the secure side? Would it be easier for you print the backtrace from the secure side?

I'm not immediately familiar with the "ROM code RPC handlers" but you you should be able to setup the non-secure handler context and exception-return to it, although I do not have a specific example matching your use-case on hand.

Andrew

Hi Andrew,

thank you for your response.

I attempted to "manually" switch to non-secure mode and then call my handler code. Return to secure mode will happen via SMC instruction.

Unfortunately, I had to learn that it's not so easy to switch from secure mode to non-secure mode, sunce the code (in PPA) is running in secure memory, and after setting the "NS" bit, fetching the next instruction fails and the machine locks up :(

I also experimented with the more-or-less documented calls to register a RPC ("API_HAL_TASK_MGR_RPCINIT") and to call a RPC ("API_USR_PA_TASK_MGR_RPCCALLSTART").

Registering appears to work, but whenever I try to call an RPC, I end up at very strange places in code - but yes, somehow the MPU switches to non-secure mode. In the end, MPU typically stops with "invalid instruction" and PC=0x00000000 :(

Any advice is highly appreciated.

Regards,

Jürgen

Hi

we have not exercised this path - i am trying to check if we can have additional suggestions from our side

Jürgen

I  checked, and we have not tried this path before and dont think i have any additional pointers to make progress.

Is this still blocking your work or have you been able to get around it

Hi Sriram,

thank you for you response, even if it's not the kind I was hoping for. BTW: I got almost identical reply from your colleague Daniel Allred.

And yes, I'm still stuck with my attempts to get the hard lockup detection working. 

I achieved to set up the timer, and receive the FIQ in the secure world (i.e. PPA), but I completely failed to have related the Linux code to handle the FIQ executed (in non-secure world).

Regards,

Jürgen