new dma API questions

[Dan Malek]

On Jun 3, 2004, at 5:06 AM, Pantelis Antoniou wrote:


> 1. dma_map_single finally calls virt_to_bus, which is simplified
>   to:
>      return (unsigned long)address - KERNELBASE + PCI_DRAM_OFFSET;
>
>   PCI_DRAM_OFFSET is defined to be pci_dram_offset.
>   Typically it is set be 0 for most arches without pci.

It's typically set to zero for all architectures.

>   How could we overide it with a constant 0 so that we avoid the
>   memory access?

What memory access?

> 2. How soon in the init sequence could we call dma_alloc_consistent?

Not soon enough.

>   For example when setting up a serial console on 8xx I need memory
>   for the fifos, and I have to revert in using m8xx_hostalloc which
>   IMO should be already dead.

As you pointed out, that is going to have to stay for a while.  The
CPM and peripherals must do DMA long before the generic
supporting functions are ready.

>   If we could arrange for consistent_alloc to be able to operate with
>   a fixed memory area until the memory initialization is complete
>   it would make my life much easier and we could finally kill
>   m8xx_hostalloc & friends.

I don't think it is worth the complication.


	-- Dan


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