On Mon, Feb 17, 2014 at 07:06:37PM +0100, Stanislav Meduna wrote: > 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.
Have you tried the uio_dmem_genirq.c driver? Or are you writing a new one? > 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. The uio_dmem_genirq.c driver showed up in 3.8, so it might be good for you to update your kernel if you want to do DMA memory with a UIO driver, as lots of other things in this area was fixed to accomplish this. Hope this helps, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
