Hi, all
Here is two questions about USB drvier in kernel 2.4.20
1. In the usb-ohci.c, buffer for TD is allocated as below:
data = pci_map_single (ohci->ohci_dev,
urb->transfer_buffer, data_len,
usb_pipeout (urb->pipe)
? PCI_DMA_TODEVICE
: PCI_DMA_FROMDEVICE
);
and then td is filled in to the corresponding place. My question is 1)
how DMA is actually performed? I didnt see any code to perform the
DMA. 2) How DMA controller is physically connected to the USB OHCI
host controller. Since I am working for non-pci host controller, I am
not familiar with PCI.
2) Both usb.c and usb-skeleton.c register their drivers(more specificly,
fops) with USB_MAJOR major nuber, which is
180. When a process open the device, e.g. /usb/skelx, Which open(),
usb_open() or skel_open(), is actually called? I can guess that would
be usb_open(), but dont know why. Can anyone give the answer and tell
why it works like this way.
Thanks a lot
Li Xinyi
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