How to replace bus_to_virt()?

[Stefan Richter]

Hi all,

is there a *direct* future-proof replacement for bus_to_virt()?

It appears there are already architectures which do not define a 
bus_to_virt() funtion or macro. If there isn't a direct replacement, is 
there at least a way to detect at compile time whether bus_to_virt() exists?

I am asking because the sbp2 driver uses bus_to_virt() if 
CONFIG_IEEE1394_SBP2_PHYS_DMA=y. I would like to replace this option by 
an automatic detection when the respective code in sbp2 is actually 
required.

The current implementation is this: Sbp2 uses bus_to_virt() to map from 
1394 bus addresses (which are currently identical to local host bus 
addresses) to virtual addresses. These addresses are supplied by SBP-2 
target devices and point to *arbitrary* locations within buffers. These 
buffers are supplied by the SCSI subsystem/ block IO subsystem. That is, 
sbp2 has no influence on the location of the buffers, nor has it 
influence on the location of the chunk of data which an SBP-2 target is 
reading or writing at a particular moment. But thanks to bus_to_virt(), 
sbp2 does not need to know which SCSI command buffer (and to which 
scatter/gather element in the buffer) a particular data transfer belongs to.

From what I found out so far, I am afraid I have to implement a totally 
different address mapping scheme for the cases where physical DMA is not 
available; i.e. a scheme that enables sbp2 to look up the s/g element to 
which a transfer is directed, based on the 1394 bus address of the transfer.
--
Stefan Richter
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http://arcgraph.de/sr/
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