Messages in this thread | | | Subject | Re: PCIe device driver question | From | "V.Radhakrishnan" <> | Date | Fri, 01 Aug 2008 02:17:45 +0530 |
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Thanks Robert !
Unfortunately, I cannot test this with recent kernels, since this was a WiMAX card based on a CardBus inteface and the Toshiba laptop I have has only 512 MB RAM ( though I have PCs with more RAM, the PCs don't have a CardBus interface ).
BRgds
RK
On Thu, 2008-07-31 at 12:52 -0600, Robert Hancock wrote: > 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/
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