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
-=====-=-==- -=-- ====-
http://arcgraph.de/sr/
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