Re: Problem with DMA on x86_64 with 3 GB RAM

[Andi Kleen]

Larry Finger <Larry.Finger@xxxxxxxxxxxx> 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.

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