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Date: Thu, 26 Nov 2009 16:30:25 +0100
From: Albert Herranz <albert_herranz@yahoo.es>
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [RFC PATCH 11/19] powerpc: gamecube/wii: flipper interrupt
	controller support
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Benjamin Herrenschmidt wrote:
> On Sun, 2009-11-22 at 23:01 +0100, Albert Herranz wrote:
> 
>> +static void flipper_pic_mask_and_ack(unsigned int virq)
>> +{
>> +	int irq = virq_to_hw(virq);
>> +	void __iomem *io_base = get_irq_chip_data(virq);
>> +
>> +	clear_bit(irq, io_base + FLIPPER_IMR);
>> +	set_bit(irq, io_base + FLIPPER_ICR);
>> +}
> 
> Do not use clear_bit and set_bit on IOs. They will do lwarx/stwcx. which
> is really not what you want. You can use __clear_bit and __set_bit but
> it's still fishy. Those operate on unsigned long, so the size vary
> between 32 and 64 bit etc... not something you care that much about, but
> it's still the wrong tool for the job.
> 
> Do those guys have more than 32 interrupts ? If not, just hand
> code the msak & shifts. If they do, then maybe stick with __clear_bit()
> and __set_bit() which are the non atomic variants.
> 

There can be only 32 interrupt sources per pic.
I'll build a mask and check if just a simple write works too (it should IMHO), instead of a RWM.

> Cheers,
> Ben.
> 

Thanks,
Albert