Re: Problem with DMA on x86_64 with 3 GB RAM

[Larry Finger <Larry.Finger@lwfinger.net>]

Andi Kleen wrote:
> Larry Finger <Larry.Finger@lwfinger.net> writes:
>
> > I am trying to debug a bcm43xx DMA problem on an x86_64 system with 3
> > GB RAM. Depending on the particular chip and its implementation, dma
> > transfers may use 64-, 32-, or 30-bit addressing, with the problem
> > interface using 30-bit addressing. From test prints, the correct mask
> > (0x3FFFFFFF) is supplied to pci_set_dma_mask and
> > pci_set_consistent_dma_mask. Neither call returns an error. In
> > addition, several x86_64 systems with more than 1 GB RAM have worked
> > with the current code.
>
> 30bit DMA has be bounced through GFP_DMA. The driver needs special
> code for this. You can look at the b44 driver for a working reference.
>
> The pci_dma_* interfaces on x86-64 only support masks >= 0xffffffff,
> anything smaller has to be handled manually.

Thanks for the info. I obviously get to devote some effort to seeing how the b44 code handles the 
same problem.

Shouldn't this problem be mentioned somewhere in the documentation, or did I miss something?

Larry
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/