Re: [PATCH v2 3/6] hppa: Add support for an emulated TOC/NMI button.

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Helge & Richard,

Nevermind the missed review comments, I'm revisiting this
patch while looking at building libtcg-hppa.so.

On 1/2/22 00:56, Philippe Mathieu-Daudé wrote:
> On 31/1/22 22:35, Helge Deller wrote:
>> Almost all PA-RISC machines have either a button that is labeled with 
>> 'TOC' or
>> a BMC/GSP function to trigger a TOC.  TOC is a non-maskable interrupt 
>> that is
>> sent to the processor.  This can be used for diagnostic purposes like 
>> obtaining
>> a stack trace/register dump or to enter KDB/KGDB in Linux.
>>
>> This patch adds support for such an emulated TOC button.
>>
>> It wires up the qemu monitor "nmi" command to trigger a TOC.  For that it
> 
> s/qemu/QEMU/ (few others).
> 
>> provides the hppa_nmi function which is assigned to the 
>> nmi_monitor_handler
>> function pointer.  When called it raises the EXCP_TOC hardware 
>> interrupt in the
>> hppa_cpu_do_interrupt() function.  The interrupt function then calls the
>> architecturally defined TOC function in SeaBIOS-hppa firmware (at 
>> fixed address
>> 0xf0000000).
>>
>> According to the PA-RISC PDC specification, the SeaBIOS firmware then 
>> writes
>> the CPU registers into PIM (processor internal memmory) for later 
>> analysis.  In
> 
> Typo "memory".
> 
>> order to write all registers it needs to know the contents of the CPU 
>> "shadow
>> registers" and the IASQ- and IAOQ-back values. The IAOQ/IASQ values are
>> provided by qemu in shadow registers when entering the SeaBIOS TOC 
>> function.
>> This patch adds a new aritificial opcode "getshadowregs" (0xfffdead2) 
>> which
> 
> Typo "artificial".
> 
>> restores the original values of the shadow registers. With this opcode 
>> SeaBIOS
>> can store those registers as well into PIM before calling an 
>> OS-provided TOC
>> handler.
>>
>> To trigger a TOC, switch to the qemu monitor with Ctrl-A C, and type 
>> in the
>> command "nmi".  After the TOC started the OS-debugger, exit the qemu 
>> monitor
>> with Ctrl-A C.

IIUC you are abusing TOC to communicate with SeaBIOS, filling
iaoq_f with SeaBIOS-specific 0xf0000000, unrelated to the pa2.0
spec; is that correct?

I'm trying to see how to integrate firmware specific knowledge
into libtcg-hppa.so which is supposed to be only architectured
parts (usually we handle firmware stuffs in machine code, not
translation one).

Regards,

Phil.

>> Signed-off-by: Helge Deller <deller@gmx.de>
>> ---
>>   hw/hppa/machine.c        | 35 ++++++++++++++++++++++++++++++++++-
>>   target/hppa/cpu.c        |  2 +-
>>   target/hppa/cpu.h        |  5 +++++
>>   target/hppa/helper.h     |  1 +
>>   target/hppa/insns.decode |  1 +
>>   target/hppa/int_helper.c | 19 ++++++++++++++++++-
>>   target/hppa/op_helper.c  |  7 ++++++-
>>   target/hppa/translate.c  | 10 ++++++++++
>>   8 files changed, 76 insertions(+), 4 deletions(-)
>> +static const TypeInfo machine_hppa_machine_init_typeinfo = {
>> +    .name = ("hppa" "-machine"),
> 
>         .name = MACHINE_TYPE_NAME("hppa"),
> 
>> +    .parent = "machine",
>> +    .class_init = machine_hppa_machine_init_class_init,
>> +    .interfaces = (InterfaceInfo[]) {
>> +        { TYPE_NMI },
>> +        { }
>> +    },
>> +};