linux-kernel - Re: 2.6.29-rc libata sff 32bit PIO regression

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Date:	Sat, 31 Jan 2009 16:06:01 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Hugh Dickins <hugh@...itas.com>, Jeff Garzik <jgarzik@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.29-rc libata sff 32bit PIO regression

O> > +	ata_for_each_dev(adev, &ap->link, ENABLED) {
> > +		if (adev->class == ATA_DEV_ATAPI)
> > +			fifo = 0;
> > +	}
> >   
> 
>    Er, couldn't we do that dynamically, based on which device is 
> executing the command now?

Possibly but PCI command cycles are expensive so you'd want to cache the
state and stuff. Better to get it correct firstly.
 
> > +	if (pdev->device == PCI_DEVICE_ID_AMD_VIPER_7411) /* FIFO is broken */
> > +		fifo = 0;
> > +
> > +	/* On the later chips the read prefetch bits become no-op bits */
> > +	pci_read_config_byte(pdev, 0x41, &r);
> > +	r &= ~fifobit[ap->port_no];
> >   
> 
>   Why not:
> 
>        r &= ~fifo;

Because then it wouldn't clear the bits if they were set already and we
wanted them off!
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