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authorDavid S. Miller <davem@davemloft.net>2005-06-02 15:55:50 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2005-06-28 00:52:45 -0400
commite24c2d963a604d9eaa560c90371fa387d3eec8f1 (patch)
tree66be193d59dd22fac0b62980769c4f19e045b5a2 /include/asm-alpha/pci.h
parent2311b1f2bbd36fa5f366a7448c718b2556e0f02c (diff)
[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 <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'include/asm-alpha/pci.h')
-rw-r--r--include/asm-alpha/pci.h17
1 files changed, 17 insertions, 0 deletions
diff --git a/include/asm-alpha/pci.h b/include/asm-alpha/pci.h
index 0c7b57bc043a..6c71dc1ad4ca 100644
--- a/include/asm-alpha/pci.h
+++ b/include/asm-alpha/pci.h
@@ -223,6 +223,23 @@ pci_dac_dma_sync_single_for_device(struct pci_dev *pdev, dma64_addr_t dma_addr,
223 /* Nothing to do. */ 223 /* Nothing to do. */
224} 224}
225 225
226static inline void pci_dma_burst_advice(struct pci_dev *pdev,
227 enum pci_dma_burst_strategy *strat,
228 unsigned long *strategy_parameter)
229{
230 unsigned long cacheline_size;
231 u8 byte;
232
233 pci_read_config_byte(pdev, PCI_CACHE_LINE_SIZE, &byte);
234 if (byte == 0)
235 cacheline_size = 1024;
236 else
237 cacheline_size = (int) byte * 4;
238
239 *strat = PCI_DMA_BURST_BOUNDARY;
240 *strategy_parameter = cacheline_size;
241}
242
226/* TODO: integrate with include/asm-generic/pci.h ? */ 243/* TODO: integrate with include/asm-generic/pci.h ? */
227static inline int pci_get_legacy_ide_irq(struct pci_dev *dev, int channel) 244static inline int pci_get_legacy_ide_irq(struct pci_dev *dev, int channel)
228{ 245{