On Wed, 2001-12-19 at 10:56, Geoffrey Espin wrote: > > > > What's wrong with GFP_DMA ? Doesn't it solve exactly this problem ? > > Personally I don't like the hack but you have to ask what he needs. > > kmalloc grabs memory from the CPU cache. GFP_DMA insures that cache memory > > is continues. I think Geoffrey needs to use a specific memory address in > > PCI space. Tho I like Geoffrey to try using GFP_DMA. The reason I don't > > like the hack is that skbuff's is bus independent. Not all ethernet cards > > are PCI based. Please try using GFP_DMA and let us know if it worked. > > Yes, I originally thought this was what addressed it. > Is "setting dma_mask" what is meant by "using GFP_DMA"? > > The problem is drivers call dev_alloc_skb() which can allocate > memory anywhere in (my 32M) memory. > > The PCI host controller part of the uPD98052 with its VR4120a core > (doc at http://www.idiom.com/~espin/nec/hwdoc/uPD98502-UM.pdf) > allows you to program a 4M window onto DRAM. I use top 4M of 32M, > but it's arbitrary. Then only this area can be transferred to > by/from the PCI devices. So its not the PCI devices that is the > problem, but access to the host-side DRAM. > > Currently, my private pci_alloc/free_consistent() routines manage > the 4M at top of memory (its not added to kernel with > add_memory_region() in prom.c). > > With these hacks (including net/core/skbuff.c:alloc_skb->pci_alloc_consistent) > I've been successfully using the Tulip Ethernet (LinkSys) card (with no > changes to the driver). FYI, this is not an isolated issue. We deal with a number of architectures and we've seen this problem with other arches and system controllers as well. A 'generic' solution would be nice and probably necessary at some point. 2.5 would be a good place to do it, if only someone would volunteer ;-) Pete
