Re: [PATCH 2 of 13] ipath - set up 32-bit DMA mask if 64-bit setup fails

[Segher Boessenkool <segher@kernel.crashing.org>]

>     Bryan> Some systems do not set up 64-bit maps on systems with 2GB
>     Bryan> or less of memory installed, so we have to fall back to
>     Bryan> trying a 32-bit setup.
>
> Which systems does this happen on?

PowerPC with U3 or U4 northbridge, i.e. Maple or PowerMac G5 systems.
If the IOMMU (DART) is disabled, we have a 32-bit only DMA mask.  The
DART will be disabled by default if there is 2GB or less of memory (as
it isn't needed then).

> I'm just curious, because mthca has
>
> 	err = pci_set_dma_mask(pdev, DMA_64BIT_MASK);
> 	if (err) {
> 		dev_warn(&pdev->dev, "Warning: couldn't set 64-bit PCI DMA mask. 
> \n");
>
> and I've never had a single report of that warning triggering.

That's only because I never used those cards on systems with fewer
than 4GB of memory :-)


Segher

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