Re: [parisc-linux] tulip DMA mapping

[Matthew Wilcox <matthew@wil.cx>]

On Thu, Nov 09, 2000 at 12:12:25PM -0800, Grant Grundler wrote:
> 0 is a valid pci_map_single() return value when the system has an IO MMU.

Oh dear.  You can bet tulip won't be the only driver which assumes it
isn't a valid return value.  Can't our IOMMU code be limited in such a
way that 0 is not a valid return value?  Say, constrain all allocated
addresses to the top half of the device bus?

(um, just check me on this, map_single returns a device bus address,
not a processor bus address, right?)

> The system will panic before pci_map_single() will fail.
> The driver needs to remember some other way if a buffer was mapped or not.
> Or the Documentation/DMA-mapping.txt should be changed - ie add this
> to the interface definition and I can reserve the 1st mapping
> entry so no-one uses it.

we should probably have a BAD_DMA_ADDR define which that array should be
initialised to.  it's a little late in 2.4 to go through and audit all
the drivers again.

> Should I be mailing Jeff Garzik <jgarzik@mandrakesoft.com> directly?
> Or can someone who knows Jeff point this out to him?

i've cc'd jeff & dave miller on this.

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