Subject: Re: [PATCH 6/8] fsldma: simplify IRQ probing and handling

From: Scott Wood <[email-masked]>
Date: Wed, 06 Jan 2010 14:51:30 -0600

Ira W. Snyder wrote:
> I don't think this would break any existing hardware. The 83xx all
> shares one IRQ line, and the 85xx/86xx only have per-channel interrupts,
> right? (I'm not an 85xx/86xx guy, I've only got 83xx experience). This
> is what the device trees suggest, anyway.

Right.

>> It looks like the other problem is that the controller interrupt handler
>> is assuming only one bit will be set in the summary register.  It should
>> call the channel handler for each bit that is set.
>>
> 
> Ok. I thought about doing this, but my changed approach seemed easier.
> 
> On the 83xx, we should only need to call the per-channel handler once
> for each group of 8 bits. The original code used ffs(), which seems a
> little wrong. Why call the handler twice if both EOSI and EOCDI are set
> for a channel?

Sorry, I meant call it once per channel that has bits set.

> Should I use a loop + mask, or is there some other neat
> trick I can use?

After you process one channel, it shouldn't have any bits set (and if it 
does, it's a new event that needs to be processed), so you could use the 
current ffs approach with a while (summary reg != 0) loop around it.

> Ok. All of the in-tree 83xx device trees have 5 interrupts listed. With
> the changes described above, we'll only call request_irq() once in that
> case, and use the per-controller interrupt.
> 
> I'll leave the documentation alone, with the exception of marking the
> per-controller interrupt optional.

Hmm, that description is specific to 83xx, and such chips really should 
have the controller interrupt specified.  The per-channel interrupt 
should not be optional, though.

-Scott