linux-kernel - Re: ->ack_intr in m68k IDE drivers [was: Re: [PATCH 2/5] ide: ->ide_dma_clear_irq() -> ->clear

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Message-ID: <4A16FABC.3010906@ru.mvista.com>
Date:	Fri, 22 May 2009 23:19:24 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-m68k@...ts.linux-m68k.org, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: ->ack_intr in m68k IDE drivers  [was: Re: [PATCH 2/5] ide: ->ide_dma_clear_irq()
 -> ->clear_irq()]

Bartlomiej Zolnierkiewicz wrote:

>>>>  It may also be worth considering turning this method into 
>>>>test-and-clear, so that we can get the actual IDE interrupt state on 
>>>>the chips that implement this...

>>>  Probably might add the test_irq() method to be called on 
>>>!hwif->waiting_for_dma. Cleraing the status at once seems impractical...

>>    Yet this seems what ack_intr() method is doing already...
>>    What it does is testing IRQ status and "acknowledging" it (the semantics 
>>of "acknowledge" is not clear to me, yet it seems that it's clearing the 
>>interrupt latch in the drivers where it's implemented). And the call site of 
>>ack_intr() method corresponds to where test_irq() should have been called, 
>>so it seems we don't need yet another method and probably didn't even need 
>>clear_irq() method in the first place?..

> They have different goals -- the main purpose of ack_intr() (despite its name)
> seems to be testing whether the IRQ is ours,

    It does clear some interrupt bit if it sees that IRQ is ours too, hence 
the name.

> OTOH in clear_irq() we know that
> already and we just want to clear the pending IRQ status.

    There seems to be duplication of functionality b/w ack_intr() and 
clear_irq() now...

> So I'm not sure if unification is desirable... though some improvements are
> definitely possibly there (less confusing naming at least)...

>>    Bart, could you clarify about how ack_intr() is supposed to work?

> Good question, m68k list would be the best place to look for an answer..

    Well, I seem to have been able to infer it from the code...

MBR, Sergei
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