Messages in this thread | | | Subject | Re: [RFC][PATCH] move dma_mask into struct device | Date | Sat, 16 Nov 2002 12:01:59 -0500 | From | "J.E.J. Bottomley" <> |
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arndb@de.ibm.com said: > On my s390 system, I can have many thousand devices and none of them > is doing DMA, so I would indeed call it architecture specific. Note > that even in a normal PC system, most devices (e.g. CPUs, input > devices or the disks attached to the host adapter) don't have any > concept of DMA.
DMA itself is pervasive to almost every architecture, that's why we have the DMA API. That some devices don't do DMA, I agree with (the struct scsi_device is another example). However, in order to divorce DMA from the PCI bus, it has to be obtainable from the generic device, without requiring knowledge of the bus. In OO terms, it would be in a dmaable_device which inherits from device, but for expediency in layering all this into the kernel means I'd have to break almost every driver and introduce them to the concept of dmaable_device, so it's just easier to expand device by a pointer.
James
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