From e24c2d963a604d9eaa560c90371fa387d3eec8f1 Mon Sep 17 00:00:00 2001 From: "David S. Miller" Date: Thu, 2 Jun 2005 12:55:50 -0700 Subject: [PATCH] PCI: DMA bursting advice After seeing, at best, "guesses" as to the following kind of information in several drivers, I decided that we really need a way for platforms to specifically give advice in this area for what works best with their PCI controller implementation. Basically, this new interface gives DMA bursting advice on PCI. There are three forms of the advice: 1) Burst as much as possible, it is not necessary to end bursts on some particular boundary for best performance. 2) Burst on some byte count multiple. A DMA burst to some multiple of number of bytes may be done, but it is important to end the burst on an exact multiple for best performance. The best example of this I am aware of are the PPC64 PCI controllers, where if you end a burst mid-cacheline then chip has to refetch the data and the IOMMU translations which hurts performance a lot. 3) Burst on a single byte count multiple. Bursts shall end exactly on the next multiple boundary for best performance. Sparc64 and Alpha's PCI controllers operate this way. They disconnect any device which tries to burst across a cacheline boundary. Actually, newer sparc64 PCI controllers do not have this behavior. That is why the "pdev" is passed into the interface, so I can add code later to check which PCI controller the system is using and give advice accordingly. Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/asm-sparc64/pci.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/asm-sparc64') diff --git a/include/asm-sparc64/pci.h b/include/asm-sparc64/pci.h index 2a0c85cd1c11..402667300d01 100644 --- a/include/asm-sparc64/pci.h +++ b/include/asm-sparc64/pci.h @@ -220,6 +220,23 @@ static inline int pci_dma_mapping_error(dma_addr_t dma_addr) return (dma_addr == PCI_DMA_ERROR_CODE); } +static inline void pci_dma_burst_advice(struct pci_dev *pdev, + enum pci_dma_burst_strategy *strat, + unsigned long *strategy_parameter) +{ + unsigned long cacheline_size; + u8 byte; + + pci_read_config_byte(pdev, PCI_CACHE_LINE_SIZE, &byte); + if (byte == 0) + cacheline_size = 1024; + else + cacheline_size = (int) byte * 4; + + *strat = PCI_DMA_BURST_BOUNDARY; + *strategy_parameter = cacheline_size; +} + /* Return the index of the PCI controller for device PDEV. */ extern int pci_domain_nr(struct pci_bus *bus); -- cgit v1.2.3