[openib-general] [PATCH 1/7] IB/core - Add DMA mapping functions to allow device drivers to interpose

[Or Gerlitz]

Ralph Campbell wrote:
> IB/core - Add DMA mapping functions to allow device drivers to interpose
> 
> The QLogic InfiniPath HCAs use programmed I/O instead of HW DMA.
> This patch allows a verbs device driver to interpose on DMA mapping
> function calls in order to avoid relying on bus_to_virt() and
> phys_to_virt() to undo the mappings created by dma_map_single(),
> dma_map_sg(), etc.

Yet another issue i see here: i understand that the core you are using 
at your HCA is capable of doing DMA but is able to do so from one RX and 
one TX cyclic descriptor buffer, correct? (*)

Hence on the RX flow, you first get the IB packet into a buffer 
allocated by the driver and then copy it to the buffer posted by the 
user to the QP. But what is going on the TX flow, per my understanding 
here you should be able to do it zero-copy wise but you do need to 
provide a **dma** (and not kernel virtual nor physical) address to the HCA.

This means that for DMA_TO_DEVICE mappings you do want to call the 
original dma_map_xxx calls and Roland's suggestion to have 
ib_dma_map_xxx calls return u64 is problematic from another aspect then 
the one i have pointed on.

Going to the SC06 and then vacationing, I will probably not be able to 
further jump on this thread before Nov 26th, anyway, my personal feeling 
is that this need to be baked a little more, specifically pushing it for 
2.6.20-rc1 might be moving too fast... but if you guys feel the open 
issues are resolved feel free to go ahead.

cheers,

Or.

(*) kernel bypass for rx/tx postings/completions by libipath seems to me 
as black magic... you have to copy the rx data from the driver cyclic 
buffer to the buffer pointed by tge user space qp wqe without passing 
through the kernel. Do you do it on the poll_cq time? how do you post tx?