Messages in this thread | | | Date | Sun, 31 Jul 2005 12:36:07 +0200 | From | Manfred Spraul <> | Subject | default values for pci dma_mask and coherent_dma_mask |
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Hi,
From Documentation/DMA-mapping.txt:
> pci_alloc_consistent() by default will return 32-bit DMA addresses. > PCI-X specification requires PCI-X devices to support 64-bit > addressing (DAC) for all transactions. And at least one platform (SGI > SN2) requires 64-bit consistent allocations to operate correctly when > the IO bus is in PCI-X mode. Therefore, like with pci_set_dma_mask(), > it's good practice to call pci_set_consistent_dma_mask() to set the > appropriate mask even if your device only supports 32-bit DMA > (default) and especially if it's a PCI-X device.
What does "good practice" mean? Is the default 32-bit on all archs or not? Recent nForce nics support 32-bit for the (coherent) ring buffer and 40-bit for the rx/tx data buffers. I intend to add these lines to the driver:
+ if (pci_set_dma_mask(pci_dev, 0x0000007fffffffffULL)) { + printk(KERN_INFO "forcedeth: 64-bit DMA failed, using 32-bit addressing for device %s.\n", + pci_name(pci_dev)); + }
Is this sufficient, or is it mandatory to add pci_set_dma_mask(,DMA_32BIT_MASK) and pci_set_consistent_dma_mask (with error handling - IMHO 10 useless lines).
-- Manfred
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