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

[Rafał Miłecki]

W dniu 26 lipca 2011 17:33 użytkownik Larry Finger
<Larry.Finger at lwfinger.net> napisał:
> 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.

Can you (anyone, not just Larry ;) ) give me some tip, how to
implement this correctly? From programming POV.

We should return two infos from ssb code now:
1) Routing bit
2) Address which should be used

Should I add new function for this? Or create struct
dma_translation_info with 2 fields? Or return array? Or...?

-- 
Rafał