linux-kernel - Re: [RFC] pata

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Date:	Sun, 08 Apr 2007 21:03:10 -0400
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Russell King <rmk+lkml@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] pata_icside driver

Alan Cox wrote:
>> The second FIXME area is ata_irq_ack - it is unconditionally coded
>> for SFF-type interfaces.  I believe that using this function in
>> non-BMDMA interfaces is wrong - it attempts to read from the BMDMA
>> registers irrespective of whether ap->ioaddr.bmdma_addr is set or
>> not.  The question this poses is: what should non-BMDMA implementations
>> use for this method?  Note that pata_platform also uses this
>> function despite not supporting BMDMA which seems even more suspicious.
> 
> Thats a bug that has arrived again. The older code was corrected to
> handle this properly but the fix appears to have become lost. The
> ioread/iowrite code actually made quite a mess (all the address reporting
> is also broken) and we do some iffy things like compare the iomap result
> with zero and assume thats the same as checking for true bus zero
> addresses.
> 
> ata_irq_ack is part of the SFF layer so its fine that it assumes SFF but
> its wrong that it is used unconditionally and it shouldn't be used this
> way. It just needs a (!ap->ioaddr.bmdma_addr) test adding (assuming thats
> valid for iomap)

No.  It does not need such a test, as it requires BMDMA, not just an 
SFF-style Status register.  It is up to the driver to decide whether or 
not ata_irq_ack() is appropriate for your hardware.

pata_icside needs its own ata_irq_ack -- which may just be as simple as 
reading the Status register to clear the interrupt condition.

If others need this as well, ata_sff_irq_ack() would be a good generic 
function to create.

	Jeff



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