On Thu, 19 Feb 2004, David S. Miller wrote:On Fri, 20 Feb 2004 18:10:41 +1100 Benjamin Herrenschmidt <[EMAIL PROTECTED]> wrote:
Hrm... so if the USB device drivers are actually doing the dma mapping
themselves, it make sense for them to pass their own struct device, no ?
That's right, at least that was the idea.
No. That would be _fundamentally_ wrong.
There's no way a USB device can do DMA in the first place. It has no DMA
controller, and no way to read/write memory except through the USB host.
So it is the host - and only the host - that matters. Anything else is a
bug.
Sure. So dma-mapping.h does this: int dma_supported(struct device *dev, u64 mask) { return device->bus->dma_supported(dev, u64 mask); }
And USB, when it creates its bus_type, does this:
int usb_dma_supported(struct device *dev, u64 mask) {
usb_dev *usbdev = to_usb_device(dev);
return usbdev->root_hub->controller->bus->dma_supported(controller, u64 mask)
}
And of then PCI has:
int pci_dma_supported(struct device *dev, u64 mask) {
pci_dev *pcidev = to_pci_dev(dev, u64 mask);
...
}
Then a USB driver uses its own usb_device->dev and it all ends up back at the PCI bus.
For PCI devices of course, device->bus->dma_supported() *is* pci_dma_supported(), so there's no middleman (as USB is above).
-- Hollis Blanchard IBM Linux Technology Center
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