Re: [Qemu-devel] [RFC PATCH] Distinguish between reset types

[Anthony Liguori]

David Woodhouse <address@hidden> writes:

> On Tue, 2013-02-19 at 16:17 -0600, Anthony Liguori wrote:
>> Right, this is what's strange to me.  There's no hardware analog AFAICT
>> so I'm not sure why we're exposing it as a qemu_irq other than we want
>> to jump through a function pointer invocation instead of making a
>> straight funciton call :-)
>
> Hey, don't ask me. I was just trying to do what Paolo said in response
> to me first attempt — which just accessed the 'hard reset' flag in the
> PIIX directly from the I440FX reset handler.
>
>> > That just sets a flag to say that the coming *system* reset is a hard
>> > reset and not a soft reset.
>> 
>> Yes, but this flag is in PIIX, not the i440fx.
>
> Yes. The Reset Control Register is in the PIIX. And the i440fx just
> happens to be the only other device that *cares* if it's a hard reset or
> a soft reset. For now. Thankfully they're implemented in the same C file
> and even initialised together, which lets us do a special-case hack
> relatively easily.
>
>> I suspect what we need to do is convert qemu_system_reset_request() into
>> a qemu_system_cpu_reset() that takes a callback.  Once the VCPUs have
>> been reset, the callback can then be used to reset all or some of the
>> device model.  This of course means removing the reset handlers in the
>> CPUs as they exist today.
>> 
>> Cc'ing Andreas to get his thoughts.
>> 
>> FWIW, I'm not expecting you to do this to fix this issue.  Just thinking
>> out loud here really.
>
> Sounds good to me. I'm beginning to wish I'd just ignored the fact that
> we need a properly working "soft" reset to get back from 286 protected
> mode to real mode, and wired up the damn PAM reset unconditionally. I'm
> not convinced that the protected->real mode transition will work for
> anyone anyway.

Can you try out the following tree:

    git://github.com/aliguori/qemu.git soft-reset.2

Or better yet, post binaries of Tiano Core + SeaBIOS as a CSM for me to
try out?

The above implements a CPU-only soft reset that should fix the problem
you're having with PAM resetting unconditionally.  If it works, I'll
fixup the other PC callers of reset too.

Regards,

Anthony Liguori