hi all, few basic PCI doubts :- 1) What is difference between PCI I/O & Memory regions?? 2) What r these 2 regions required for?? 3) Linux's PCI subsystem provides some functions like "pci_resource_start" to get resource info. There's an arg passed to it - "int bar"(base adr. reg.). In one of the driver files i've seen for getting the I/O and Memory start addresses "bar" was passed as 0 & 1 respectively. In rubini's book it says these values can vary from 0 to 5 (for the 6 base addr. regs i guess!). what does these values signify. Does it mean BAR0 holds the start address of PCI I/O space etc.??? TIA - /dev/mandeep -----Original Message----- From: Krishnakumar. R [mailto:krishnakumar@naturesoft.net] Sent: Friday, March 05, 2004 6:30 PM To: Mandeep Singh Sandhu; kernelnewbies@nl.linux.org Subject: Re: PCI DMA info require Hi, > hi all, > i need some info as to how DMA is used by > PCI devices ex. an ethernet card, how DMA > fits in the whole picture. I think that the DMA is performed by the network card dma controller (pci dma controller). In case of RTL network cards: 1. Set the card to be dma bus master 2. we will give first allocate dma-able area using the "pci_alloc_consistent". 3. Inform the network card about this area (feed in the physical addresses to the network card registers) 4. While reception, the network would automatically perform DMA from the local buffer (of the network card) to the location which we had specified in step 1. So we need to only take the packets directly from that place (no headache of thinking about the DMA, network card will do it for us.) (This is similar in case of transmission also) >also there is a > field in the net_device struct "dma" which > holds the "DMA channel allocated by the device", > what does this mean, is a seperate DMA controller > used by each PCI device??? Hmm... looks like this member of the structure is not used in most drivers (8139too.c, ne2k-pci.c etc.) Hope that helps, Regards, KK. -- HomePage: http://puggy.symonds.net/~krishnakumar -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
