linux-kernel - Re: drivers using the non-PCI dma_set

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Date:	Mon, 22 Dec 2008 22:43:33 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	linux-kernel@...r.kernel.org
Subject:  Re: drivers using the non-PCI dma_set_mask() on PCI devices

Mikael Pettersson wrote:
> Several drivers do the following:
> 
> 	struct pci_dev *pdev = ...;
> 	...
> 	if (dma_set_mask(&pdev->dev, mask))
> 		...
> 
> But pdev->dev.dma_mask == &pdev->dma_mask, so this is essentially a
> roundabout way of saying
> 
> 	if (pci_set_dma_mask(pdev, mask))
> 
> except that it bypasses the PCI-specific operations pci_set_dma_mask()
> may do on that platform.
> 
> Drivers doing this include drivers/scsi/aic7xxx/aic79xx_osm_pci.c,
> drivers/scsi/aic7xxxx/aic7xxx_osm_pci.c, drivers/scsi/qla2xxx/qla_os.c,
> drivers/net/wireless/rt2x00/rt2x00pci.c, and drivers/media/video/meye.c.
> 
> Is it considered acceptable that drivers bypass the PCI DMA API on
> PCI devices like this, or are these drivers in error?
> 
> I'm doing some work on an embedded platform (ARM IXP4xx) with some
> PCI DMA restrictions. To handle these the platform provides its own
> versions of pci_set_dma_mask() and pci_set_consistent_dma_mask(),
> but its dma_set_mask() currently does not do anything PCI-specific.
> The question is: should dma_set_mask() have PCI knowledge or not?

AFAIK pci_set_dma_mask is somewhat deprecated, and dma_set_mask should 
be used instead. If the platform fails to do what's needed when 
dma_set_mask is called on a PCI device then it would seem the platform 
code is in error.

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