Reset iMX53-QSB from the secure world

[Stefan Kalkowski]

Hi Ofer,

On 09/10/2015 10:21 AM, Ofer Hasson wrote:
> Hey,
> 
> I'm attempting to make a simple reboot feature on Freescale's iMX53-QSB.
> I'm currently working using the tz_vmm example.
> So, I understand that the way to achieve that on this board is through the
> watchdog timer,
> I followed the Linux kernel code that does this, and implemented a kernel
> module that does only the reboot part, this what i came up with:
> -
> volatile unsigned short *wdog1_base = (volatile unsigned short*) 0xf7e98000;
> *wdog1_base = (1 << 2);
> -
> 
> This exact code, i a kernel module, does an immediate reset and i get the
> u-boot shell.
> All of this is done on the normal world of course, now i wish to have this
> in the secure world,
> Running the exact same code in the secure world, in the handle hypercall
> routine i get:
> -
> no RM attachment (faulter 129090 with IP 70014c28 attempts to write to
> address f7e98000)
> void Genode::Pager_object::unresolved_page_fault_occurred(): not implemented
> unknown signal context

The problem is that you took the virtual address the watchdog is mapped
to within the Linux kernel, and try to access that address within
Genode's HW kernel. That is why you see above page-fault message.

The kernel is running with a configured MMU too, it is not disabled
within the kernel. Moreover, the kernel does not have all physical
memory mapped one-by-one automatically.

Is there a hard constrain to do the reset within the kernel? It is much
more convenient and easy to implement for instance within the platform
driver. Because you do not need to extend the kernel syscall interface,
or need an extra session interface within core. You could extend the
platform driver interface instead.

In general, what a driver needs to do to access the Watchdog registers
is the following:

# open an IOMEM session with the corresponding physical address
  (bus address) of the watchdog device
# map the IOMEM dataspace to a free virtual memory area
# access the watchdog registers via the virtual addresses, it was
  mapped to

A convenient way is to use the Attached_mmio helper class. It does
everything for you. Moreover, the MMIO framework (used in that class)
allows you to define registers, and bit-magic in a more comprehensible
fashion.

The code to reset the board would look like the following:

  #include <os/attached_mmio.h>

  struct Watchdog : Genode::Attached_mmio
  {
       /* 16bit register at offset 0 */
       struct Control : Register<0x0, 16> {

           /* this Bitfield relates to (1 << 2) */
           struct Enable : Bitfield<2, 1> {};
       };

       /*
        * the physical address range of the watchdog has to be given to
        * the attched_mmio base class (manual says: 0x53F98000, 0x1000)
        */
       Watchdog() :  Attached_mmio(WDOG_BASE, WDOG_SIZE) {}

       void reset() { write<Control::Enable>(1); }
  };

Assuming that Linux is doing nothing more with the device, and the
device is accessable from user mode, it should work to incorporate above
snippet into the platform driver.

Best Regards
Stefan

> -
> 
> Any idea's how to achieve my reset from the secure world ?
> Also, if someone could shed some light about the error, I'm not that
> familiar with Genode, just starting to work with it.
> 
> Thanks in advanced.
> 
> 
> 
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-- 
Stefan Kalkowski
Genode Labs

http://www.genode-labs.com/ · http://genode.org/