On Fri, Nov 18, 2011 at 04:16:23PM -0500, Jean-Francois Dagenais wrote: > Hello fellow hackers. Hi. Could you please limit the line length of your mails to something less than 80 chars? > > I am maintaining a UIO based driver for a PCI-E data acquisition device. Can you post it? No point in discussing non-existent code... > > I map BAR0 of the device to userspace. I also map two memory areas, one is used to feed instructions to the acquisition device, the other is used autonomously by the PCI device to write the acquired data. > > The strategy we have been using for those two share memory areas has historically been using pci_alloc_coherent on v2.6.35 x86_64 (limited to 4MB based on my trials) and later, I made use of the VT-d (intel_iommu) to allocate as much as 128MB (an arbitrary limit) which appear contiguous to the PCI device. I use vmalloc_user to allocate 128M, then write all the physically continuous segments in a scatterlist, then use pci_map_sg which works it's way to intel_iommu. The device DMA addresses I get back are contiguous over the whole 128M. Neat! Our VT-d capable devices still use this strategy. > > This large memory is mission-critical in making the acquisition device autonomous (real-time), yet keep the DMA implementation very simple. Today, we are re-using this device on a CPU architecture that has no IOMMU (intel E6XX/EG20T) and want to avoid creating a scatter-gather scheme between my driver and the FPGA (PCI device). > > So I went back to the old pci_alloc_coherent method, which although limited to 4 MB, will do for early development phases. Instead of 2.6.35, we are doing preliminary development using 2.6.37 and will probably use 3.1 or more later. The cpu/device shared memory maps (1MB and 4MB) are allocated using pci_alloc_coherent and handed to UIO as physical memory using the dma_addr_t returned by the pci_alloc func. > > The 1st memory map is written to by CPU and read from device. > The 2nd memory map is typically written by the device and read by the CPU, but future features may have the device also read this memory. > > My initial testing on the atom E6XX show the PCI device failing when trying to read from the first memory map. Any kernel messages in the logs that could help? [...] Thanks, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
