Hi, what is the correct way for a UIO driver to pass a memory allocated using dma_alloc_coherent to userspace? I have googled for examples but I was not able to find a definitive answer.
My device needs two 128 kB chunks of DMA-able memory. First I tried pdev->tx_vaddr = dma_zalloc_coherent(&dev->dev, pdev->dma_len, &pdev->tx_paddr, GFP_KERNEL | GFP_DMA); info->mem[2].name = "txdma"; info->mem[2].addr = (phys_addr_t) pdev->tx_vaddr; info->mem[2].size = pdev->dma_len; info->mem[2].memtype = UIO_MEM_LOGICAL; This seemed to work at the first try, but tends to panic in various ways when unmapping. It probably only maps the first page or something like that and accessing past some limit overwrites something. If I change this to info->mem[2].addr = (phys_addr_t) pdev->tx_paddr; info->mem[2].memtype = UIO_MEM_PHYS; it seems to work at least on x86 with < 4GB memory. The uio_pruss.c (or uio_dmem_genirq.c in newer kernels) do this as well. I have a bad feeling here - if I am allocating something that is a virtual memory in the kernel, I don't expect to pretend I am accessing something else. The UIO howto explicitely states that UIO_MEM_PHYS is meant for a "physical memory on your card". Is this really a recommended way of doing this and is it portable to other architectures? I am using 3.4 kernel with realtime patches. Please Cc: me when replying. Thanks -- Stano -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/