[U-Boot] [PATCH 15/21] nios2: Generic system restart support

[Scott McNutt <smcnutt@psyent.com>]

Moffett, Kyle D wrote:
> Hi!
> 
> On Mar 08, 2011, at 19:13, Scott McNutt wrote:
>> Hi Kyle,
>>
>> Kyle Moffett wrote:
>>> The Nios-II port appears to use no generic hardware capability for
>>> performing a CPU reset.  Since all of the supported boards use the exact
>>> same code to perform a jump-to-flash it goes into __arch_restart().
>>>
>>> This means that Nios-II has a no-op __arch_emergency_restart() function.
>>> If the CPU is in an invalid state then jump-to-FLASH probably won't
>>> work.
>> If the CPU state is stable enough to call __arch_emergency_restart(),
>> a jump to the reset address should be fine. In many implementations
>> the reset code is in on-chip ROM. If things get screwed up enough
>> to affect the code in on-chip ROM, it probably won't matter what
>> gets called. ;-)
> 
  ... <snip> ...

> Basically the emergency_restart() code should handle being called even in the following scenarios:
>   * Unexpected CPU exception or interrupt occurs
>   * Interrupts on or off, or *from* an interrupt or trap handler.
>   * FLASH or other peripherals in an undefined state
> 
> If that's the case for your onboard ROM then I will certainly remove the no-op emergency restart hook from this patch.

 From a practical perspective, in the case of on-chip ROM, it would be
no different than a hard reset during any of the above activities.
But please don't remove it. Your position is sound and conservative.

I haven't had time to review the entire patch set yet. I'm assuming
the __board_emergency_restart() routine is where a board can override
the default arch-specific behavior? If so, you already provided the
hooks for more daring developers. ;-)

Regards,
--Scott