Hi People!, How are you doing?
I write to you because I'm writing a driver for a Realtek8139D 10/100Mbps, just for fun and for practice my knowledge.
I spent some time reading about PCI specifications, but I have some doubts about that:
1- I/O Port or I/O memory mapping ( RTL8139 has BAR0 for I/O PORT and BAR1 for I/O Memory )
* I've read about the diferences, and since I understood, the best way to do is with memory mapping. I/O PORT has some limitations like limited instructions can be used. Do you know more about that? More diferences?
2- DMA and memory region
* When I request for the I/O memory region of pci device:
memr_start = pci_resource_start(dev, IO_MEM);
memr_end = pci_resource_end(dev, IO_MEM);
The memr_start is the address for reach the device and send data to him?
* I've seen that pci_bus_master is supported by RTL8139D:
pci_set_master(dev);
pci_read_config_word(dev, 0x4, &is_master);
pr_info("PCI_BUS_MASTER: %d\n", is_master);
it returns 111b, so it can be enabled.
Then I think I should call pci_alloc_consistent() to take a DMA address.
This DMA address is the address of the BUS (where device is). This should be the address that I have to use for incoming/outgoing data from/to the device?
I'm a little bit stuck in these terms
Could you help me?
Best Regards
Oscar
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