> V.Radhakrishnan wrote:
> >> My guess there was a bug in your DMA mapping code. I don't think kmap is
> >> what is normally used for this. I think with get_user_pages one usually
> >> takes the returned page pointers to create an SG list and uses
> >> dma_map_sg to create a DMA mapping for them.
> >
> > Looking at the actual code, I see that I had used kmap() only to obtain
> > kernel virtual addresses for the array of struct pages obtained from
> > user space by using get_user_pages.
> >
> > Subsequently, I had used dma_map_single() and dma_unmap_single() calls
> > for single buffer calls.
>
> I'm suspicious about this usage, I don't know if that will actually
> work. There is a dma_map_page call which is meant for doing a DMA
> mapping on a struct page which should likely be used instead.
>
> >
> > The code didn't have bugs IMHO since it was used for extensive stress
> > testing the initial FPGA prototype as well as the final ASIC chip ,
> > sometimes running for over 4 days non-stop without breaking.
> >
> > However, using Test Access Points on the board and using a Logic
> > Analyzer showed that DMA was NOT taking place when RAM > 896 MB was
> > used. The hardware gurus said that PCI bus cycles just didn't seem to be
> > taking place when RAM > 896 MB was used as the source OR destination
> > address.
>
> Are you sure the address being passed to the device was correct in this
> case? There should be nothing magical about 896MB from a hardware point
> of view, and the kernel in general cannot stop you from DMAing anywhere
> you like.
>
> >
> > Perhaps this was a problem in the earlier kernel(s) and has since been
> > rectified ? ( I was using 2.6.15 then ... )
> >
> > I am just curious since Sanka Piyaratna reported a 'similar' kind of
> > situation.
> >
> > Regards
> >
> > V. Radhakrishnan
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to
majordomo@vger.kernel.org
> More majordomo info at
http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at
http://www.tux.org/lkml/
