Messages in this thread | | | Date | Thu, 4 Dec 2008 10:27:22 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA |
| |
On Thu, 4 Dec 2008, Peter Zijlstra wrote: > On Wed, 2008-12-03 at 14:39 -0700, edward_estabrook@agilent.com wrote: > > > > The gist of this implementation is to overload uio's mmap > > functionality to allocate and map a new DMA region on demand. The > > bus-specific DMA address as returned by dma_alloc_coherent is made > > available to userspace in the 1st long word of the newly created > > region (as well as through the conventional 'addr' file in sysfs). > > > > To allocate a DMA region you use the following: > > /* Pass this magic number to mmap as offset to dynamically allocate a > > chunk of memory */ #define DMA_MEM_ALLOCATE_MMAP_OFFSET 0xFFFFF000UL > > ... > > Comments appreciated! > > Yuck! > > Why not create another special device that will give you DMA memory when > you mmap it? That would also allow you to obtain the physical address > without this utter horrid hack of writing it in the mmap'ed memory. > > /dev/uioN-dma would seem like a fine name for that.
I couldn't agree more. It sounds fine as a local hack for Edward to try out some functionality he needed in a hurry; but as something that should enter the mainline kernel in that form - no.
Hugh
| |