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

[Michael Büsch]

On Tue, 26 Jul 2011 10:33:30 -0500
Larry Finger <Larry.Finger at lwfinger.net> wrote:

> 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

Oh dear. I was already wondering: Man, it can't be _that_ simple to just
look at a bit to determine something as trivial as the routing bits.
I'm glad Broadcom finally managed to fix this, though.

-- 
Greetings, Michael.