On Thu, Oct 09, 2003 at 11:36:07PM +0800, Jacky Lam wrote: > > > Almost. > > > > You can not use virt_to_* on the address returned by > > pci_alloc_consistent(). > > Why?
Because virt_to_*() is only defined for staticly mapped kernel virtual addresses...consistent_alloc() is not guaranteed to return a staticly mapped kernel virtual address so you can't use virt_to_*(). It is not a generic address translation API. > By the way, this problem will only affect the consistency of dma buffer. > In my case, it will only cause wrong output sound. But my card seems don't > consume the dma and doesn't give any interrupt in return. It's fine on PC > and I can receive interrupt if I write to the card's register to force an > interrupt. What other possible porting problem can be here? Really > strange.... Endianness issues as another person pointed out. You still have to solve these address munging issues. > > You need to hold on to the dma_addr_t returned, perform > > a bus_to_virt(dma_addr_t) and then a virt_to_* will work > > on that address. > > umm....then does virt_to_phys(bus_to_virt(dma_addr_t))==dma_addr_t No, dma_addr_t is not necessary they same as the physical address. Your platform may have physical addresses mapped 1:1 with bus (PCI) addresses but that is not always the case (PReP, many peer-to-peer PCI systems. etc). > or > bus_to_virt(dma_addr_t)==pci_alloc_consistent() ? No, the virtual address you get by doing a bus_to_virt(dma_addr_t) is != to the address that will be returned by pci_alloc_consistent() (on 4xx/8xx). > > However, I'm not sure of the "PCI related memory space" you > > are referring to. "PCI memory space" has a distinct meaning > > and the virt_to_*/*_to_bus APIs don't work there. Those APIs > > are only valid for system memory that is accessible through > > inbound transactions by a PCI bus master. > > > > You can use virt_to_* on an address returned from kmalloc > > or __get_free_pages. > > I also don't understand....Could you or someone "invent" these things > kindly give some brief explaination here (especially for the reason how > consistent_alloc() is implemented)? I think it will benefit many PPC > beginner. Thanks very much. *consistent_alloc() has a "special" implementation for 4xx/8xx because they do not snoop memory access by external bus masters. In order to allocate "consistent" memory it is necessary to create a cache inhibited mapping to system memory in the vmalloc area. Virtual addresses in the vmalloc area cannot be translated using the virt_to_* APIs. There are a number of threads on this topic if you check the archives. -Matt ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
