Re: dma_alloc_coherent bug in latest ntb_tool changes

[Dave Jiang <dave.jiang@intel.com>]

On 06/07/2018 04:10 PM, Logan Gunthorpe wrote:
> Hey,
> 
> I'm just running ntb_test on recent kernels with switchtec hardware and
> found that ntb_tool and ntb_perf no longer work. I get this kernel warning:
> 
> [   64.077406] WARNING: CPU: 3 PID: 2231 at
> ./include/linux/dma-mapping.h:516 tool_mw_trans_write+0x16d/0x332 [ntb_tool]
> 
> Indicating that the dma_coherent mask is not set on the device. (Not
> sure how much testing that patch set got before it was merged upstream...)
> 
> It seems one of the changes that slipped through is that it now
> allocates DMA memory using the NTB struct device instead of the PCI
> struct device that was used before the patchset.
> 
> Seeing nothing in the NTB tree sets the coherent mask on the NTB device
> we get a warning and fail to allocate DMA-able memory.
> 
> I'm not sure the proper fix here: should we be using the NTB device for
> DMA operations or roll back to using the PCI device? It seems cleaner to
> use the NTB device but then we at least have to set the coherent_mask to
> something sane (probably safe to set it to 64bits for NTB hardware).
> However, I'm not sure if, for all arches, DMA ops depend on anything in
> the device besides the mask.
> 
> Logan
> 

I seem to recall having this discussion previously but don't remember
the outcome. I still think we should be dealing with the PCI device when
it comes to hardware stuff like DMA since that is the actual device. The
NTB device is just a an abstract device to make it work with the NTB bus
isn't it?