From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Richter Subject: How to replace bus_to_virt()? Date: Sun, 30 Apr 2006 16:52:37 +0200 Message-ID: <4454CF35.7010803@s5r6.in-berlin.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: linux-scsi@vger.kernel.org List-Id: linux-scsi@vger.kernel.org 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/