Re: [PATCH] test/qtest: Add an API function to capture IRQ toggling

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

On 13/11/23 18:33, Gustavo Romero wrote:
>>>> Currently the QTest API does not provide a function to allow capturing
>>>> when an IRQ line is toggled (raised then lowered). Functions like
>>>> qtest_get_irq() read the current state of the intercepted IRQ lines,
>>>> which is already low when the function is called, since the line is
>>>> toggled.
>>>>
>>>> This commit introduces a new function, qtest_get_irq_trigger_counter(),
>>>> which returns the number of times a given intercepted IRQ line was
>>>> triggered (raised), hence allowing to capture when an IRQ line was
>>>> toggled.
>>>>
>>>> Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
>>>> ---
>>>>   tests/qtest/libqtest.c | 12 ++++++++++++
>>>>   tests/qtest/libqtest.h |  9 +++++++++
>>>>   2 files changed, 21 insertions(+)
>>>>
>>>> diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
>>>> index f33a210861..21891b52f1 100644
>>>> --- a/tests/qtest/libqtest.c
>>>> +++ b/tests/qtest/libqtest.c
>>>> @@ -82,6 +82,7 @@ struct QTestState
>>>>       int expected_status;
>>>>       bool big_endian;
>>>>       bool irq_level[MAX_IRQ];
>>>> +    uint64_t irq_trigger_counter[MAX_IRQ];
>>>>       GString *rx;
>>>>       QTestTransportOps ops;
>>>>       GList *pending_events;
>>>> @@ -498,6 +499,7 @@ static QTestState *qtest_init_internal(const 
>>>> char *qemu_bin,
>>>>       s->rx = g_string_new("");
>>>>       for (i = 0; i < MAX_IRQ; i++) {
>>>>           s->irq_level[i] = false;
>>>> +        s->irq_trigger_counter[i] = 0;
>>>>       }
>>>>       /*
>>>> @@ -690,6 +692,7 @@ redo:
>>>>           if (strcmp(words[1], "raise") == 0) {
>>>>               s->irq_level[irq] = true;
>>>> +            s->irq_trigger_counter[irq]++;
>>
>> This is 'irq_raised_counter',
>>
>>> Not sure whether you can get some "raise" events in a row without 
>>> some "lower" events in between ... but just in case, I wonder whether 
>>> it would make sense to check whether it is really a rising edge, i.e.:
>>>
>>>             if (strcmp(words[1], "raise") == 0) {
>>>                 if (!s->irq_level[irq]) {
>>>                     s->irq_trigger_counter[irq]++;
>>>                 }
>>>                 s->irq_level[irq] = true;
>>>
>>> What do you think?
>>
>> This is 'irq_pulsed_counter'. 'irq_lowered_counter' could also be
>> useful (at least for completeness).
> 
> I understand that the code provided by Thomas actually has the exactly same
> effect as my code. This happens because a "raise" (or "low) message is
> not sent by the "server" side unless a transition state low -> high 
> happens,
> so the check 'if (!s->irq_level[irq]) { ... }' is always true. So it's 
> still
> capturing the raising state transition (as a side note, when one intercepts
> an IRQ the current state of the IRQ line is saved -- so the old IRQ 
> state is
> always valid). Therefore, also as a consequence, like Thomas said, it's not
> possible to get a 'raise' event in a row without a 'lower' event in 
> between.
> 
> Based on your comments, I gave a second thought on 'trigger' meaning. I 
> think
> 'trigger' refers to an event or action that automatically initiates a
> procedure. Since raising an IRQ line does not always mean to generate an 
> IRQ,
> since the like can be active low in a device, maybe I should avoid using
> trigger and synonymous for raising.
> 
> I think since 'toggle' means to switch back and forth between two modes or
> states, yep, it seems ok to me to use it as a synonymous for 'pulse'.

One definition of "to toggle" is:
'''
switch from one effect, feature, or state to another by using a toggle.
'''

"pulsate":
'''
expand and contract with strong regular movements.
'''

Maybe 'pulse' is simpler to understand?

> Hence, I removed the word 'trigger' from the API function name and 
> elsewhere.
> 
> Right, I think having a qtest_get_irq_lowered_counter() is better and also,
> when used together with qtest_get_irq_raised_counter(), it's possible for a
> test to check pulses on the IRQ lines.
> 
> 
>> Per Gustavo's description, he indeed wants irq_pulsed_counter (or
>> irq_toggled_counter'.
>>
> 
> That's a good point. So far I was testing just the high -> low transition,
> but in fact the most correct way to test the device is also check for
> a high -> low transition (so, yeah, indeed test a pulse).
> 
> In the device I have:
> 
> [...]
>      /*
>       * Toggle device's output line, which is connected to interrupt 
> controller,
>       * generating an interrupt request to the CPU.
>       */
>      qemu_set_irq(s->irq, true);
>      qemu_set_irq(s->irq, false);

This is qemu_irq_pulse() from include/hw/irq.h.

> }
> 
> Thus having both qtest_get_irq_{lowered,raised}_counter() allows capturing
> an IRQ toggle, for instance, as the following, where exactly 1 pulse is 
> tested:
> 
>      uint64_t num_raises;
>      uint64_t num_lows;
> 
>      while (1) {
>          if ((num_raises = qtest_get_irq_raised_counter(qts, 0))) {
>              num_lows = qtest_get_irq_lowered_counter(qts, 0);
>              if (num_raises == num_lows && num_lows == 1) {
>                  printf("Detected correct number of pulses.\n");
>                  return 0;
>              } else {
>                  printf("Detected incorrect number of pulses.\n");
>                  return 1;
>              }
>          }
>      }
> 
>>>
>>>>           } else {
>>>>               s->irq_level[irq] = false;
>>>>           }
>>>
>>> Anyway:
>>> Acked-by: Thomas Huth <thuth@redhat.com>
> I'm sending a v2 with qtest_get_irq_lowered_counter().
> 
> Thanks!
> 
> 
> Cheers,
> Gustavo