linux-kernel - Re: libata & no PCI: dma_[un]map

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Message-ID: <20070605141714.GA2572@flint.arm.linux.org.uk>
Date:	Tue, 5 Jun 2007 15:17:14 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	David Miller <davem@...emloft.net>, mroos@...ux.ee,
	linux-kernel@...r.kernel.org
Subject: Re: libata & no PCI: dma_[un]map_single undefined

On Tue, Jun 05, 2007 at 09:56:08AM -0400, Jeff Garzik wrote:
> On Tue, Jun 05, 2007 at 12:22:18PM +0100, Alan Cox wrote:
> > > NAK
> > > 
> > > We have generic devices and generic DMA mapping.  libata already uses
> > > the generic stuff.  Now fix the platform...
> > 
> > Nice theory but your generic helpers rely on the map functions working
> > even for generic hardware that doesn't need them, so at the very least
> > there is some clean up required.
> 
> Sure there is some clean up needed -- on the arch side.
> 
> Even !PCI dma_xxx wrappers that do nothing more than return a dma
> mapping error are a valid platform implementation.

If you don't have DMA capabilities, does libata still need ->pad and
->pad_dma set?

I had a problem where a pata_platform device which wasn't DMA capable
failed to initialise because we quite rightfully made dma_alloc_coherent()
fail (due to the DMA masks not being set.)

It seems odd that libata requires DMA memory for non-DMA capable devices...

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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