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.