> IMHO it's strange that struct device.dma_mask is a pointer instead of a > plain u64. The reason this was done back then is described in > 8ab1bc19e974fdebe76c065fe444979c84ba2f74[1]: > > Attached is a patch which moves dma_mask into struct device and cleans up the > scsi mid-layer to use it (instead of using struct pci_dev). The advantage to > doing this is probably most apparent on non-pci bus architectures where > currently you have to construct a fake pci_dev just so you can get the bounce > buffers to work correctly. > > The patch tries to perturb the minimum amount of code, so dma_mask in struct > device is simply a pointer to the one in pci_dev. However, it will make it > easy for me now to add generic device to MCA without having to go the fake pci > route. Yeah, that's a strange design. As the commit log said, it's due to the historical reason. We invented the pci dma model first then moved to the generic dma model. > As I work on such a non-pci bus architecture it's still ugly that this > is a pointer because I have to allocate extra memory for that. The popular trick to avoid allocating the extra memory for that is: device.dma_mask = &device.coherent_dma_mask; > Is there a reason not to get rid of struct pci_dev.dma_mask and use > struct pci_dev.dev.dma_mask instead? (Well apart from the needed > effort of course.) > > If not, the following would be needed: > > - remove struct pci.dma_mask > - make struct device.dma_mask an u64 (instead of u64*) > - substitue var.dma_mask by var.dev.dma_mask for all > struct pci_dev var > - substitue var.dma_mask by &(var.dma_mask) for all > struct device var > > and note that there are statically initialized struct device (and maybe > struct pci_dev?) that need fixing, too. (e.g. > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/arm/mach-mx2/devices.c;h=a0aeb8a4adc19ef419a0a045ad3b882131597106;hb=HEAD#l265 > ) That's exactly the perturbation that the commit log refers to. We need to modify all the struct device at a time. We could, however, I don't think that it's worth doing. Little gain. > Additionally this could be done for struct device.dma_parms. Yeah, we should have all the dma parameters in dma_parms. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
