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Date: Fri, 27 Nov 2009 18:27:16 +0100
From: Albert Herranz <albert_herranz@yahoo.es>
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To: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [RFC PATCH 11/19] powerpc: gamecube/wii: flipper interrupt
	controller support
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Segher Boessenkool wrote:
>>>>>>> +/*
>>>>>>> + * Each interrupt has a corresponding bit in both
>>>>>>> + * the Interrupt Cause (ICR) and Interrupt Mask (IMR) registers.
>>>>>>> + *
>>>>>>> + * Enabling/disabling an interrupt line involves asserting/clearing
>>>>>>> + * the corresponding bit in IMR. ACK'ing a request simply involves
>>>>>>> + * asserting the corresponding bit in ICR.
>>>>>>> + */
>>>>
>>>> I looked it up in YAGCD; it says that _reading_ the ICR reg already
>>>> acks all interrupts (and clears the bits), you never write this reg!
>>>
>>> YAGCD is not always right. You should not take it as _the truth_.
>>
>> Oh I know.  But I have no better source of information.  Well I could
>> actually test it, that's very easy using OF :-)  Let's do that.
> 
> I tested it.  It turns out that neither reading or writing this register
> does anything; the bits are automatically cleared when the source
> deasserts.
> 

I checked it too on the Nintendo GameCube making the ack a no-op.

It turns out that we _need_ to ack the RSW (Reset Switch) interrupt.
The other interrupt sources checked (EXI, VI, DI, AI, DSP/ARAM) need no explicit ack.

> I didn't test all interrupts, some are harder to generate "on demand" than
> others.
> 

Thanks,
Albert