Problem with understanding DMA on some machines (known solution!), specs needed?

[Larry Finger]

On 07/26/2011 03:24 AM, Rafał Miłecki wrote:
> W dniu 25 lipca 2011 23:54 użytkownik Rafał Miłecki<zajec5 at gmail.com>  napisał:
>> Now, the question: when for real we should use such a solution?
>>
>> Larry, could you check your driver? Can you see anything about this?
>> Is this maybe PCI (not PCIe!) specific?
>
> I've checked thread "Interesting 14e4:4321". It seems both: 14e4:4321
> and 14e4:4322 are using PCI slot and both are not working in DMA mode.
> I start believing it's PCI specific.
>
> If you take a look at current ssb code and defines:
>> if (ssb_read32(dev, SSB_TMSHIGH)&  SSB_TMSHIGH_DMA64)
>> 	return SSB_PCIE_DMA_H32;
>> else
>> 	return SSB_PCI_DMA;
> You can see 0x80000000 (SSB_PCIE_DMA_H32) has actually "PCIE" in it's
> name. This can be true that 0x80000000 is *only* for *64-bit DMA* on
> *PCIe*.

That is almost correct. This time I found it. The pseudo code is:

dma_addr_lo = 0
dma_addr_hi = 0
if PCI || PCIe
	if PCIe && 64-bit DMA
		dma_addr_hi = 0x80000000
	else
		if chipID is 0x4322, 43221, 43231, or 43222
			dma_addr_lo = 0x80000000
		else
			dma_addr_lo = 0x40000000    <== your case

Thus it is just a little more complicated than a PCI/PCIe split, as it also 
depends on the chip ID.

I'll add this to the specs.

Larry