linux-kernel - Re: [PATCH v2 -mm 1/2] add the device argument to dma_mapping

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Date:	Wed, 2 Jul 2008 12:18:40 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, amit.shah@...ranet.com,
	muli@...ibm.com, alexisb@...ibm.com, andi@...stfloor.org,
	kvm-devel@...ts.sourceforge.net, avi@...ranet.com
Subject: Re: [PATCH v2 -mm 1/2] add the device argument to dma_mapping_error

On Wednesday 02 July 2008 12:07:23 Andrew Morton wrote:
> On Mon, 19 May 2008 15:31:28 +0900 FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
> 
> > dma_mapping_error doesn't take a pointer to the device unlike other
> > DMA operations. So we can't have dma_mapping_ops per device.
> > 
> > Note that POWER already has dma_mapping_ops per device but all the
> > POWER IOMMUs use the same dma_mapping_error function. x86 IOMMUs use
> > different dma_mapping_error functions. So dma_mapping_error needs the
> > device argument.
> 
> This patch continues to turn my hair grey.
> 
> I'm currently staring at this, in include/linux/ssb/ssb.h:
> 
> static inline int ssb_dma_mapping_error(struct ssb_device *dev, dma_addr_t addr)
> {
> 	switch (dev->bus->bustype) {
> 	case SSB_BUSTYPE_PCI:
> 		return pci_dma_mapping_error(dev->dev, addr);
> 	case SSB_BUSTYPE_SSB:
> 		return dma_mapping_error(dev->dev, addr);
> 	default:
> 		__ssb_dma_not_implemented(dev);
> 	}
> 	return -ENOSYS;
> }
> 
> How do I go from an ssb_device* to a pci_dev*?
> 
> Dunno.  I think I'll cheat and do:
> 
> static inline int ssb_dma_mapping_error(struct ssb_device *dev, dma_addr_t addr)
> {
> 	switch (dev->bus->bustype) {
> 	case SSB_BUSTYPE_PCI:
> 		return dma_mapping_error(dev->dev, addr);

The statement above is wrong. The PCI-specific dma-mapping-error function
must be used here. (I hope such a thing exists. Otherwise the API is broken).
So
		return pci_mapping_error(dev->bus->host_pci, addr);

> 	case SSB_BUSTYPE_SSB:
> 		return dma_mapping_error(dev->dev, addr);
> 	default:
> 		__ssb_dma_not_implemented(dev);
> 	}
> 	return -ENOSYS;
> }



-- 
Greetings Michael.
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