On Mon, Nov 16, 2009 at 06:12:22PM +0100, Takashi Iwai wrote:
Actually, this has been a looong-standing problem. I have a series of patches to fix these issues, but it's more intensively involved with dma_*() functions.
The patches can be found in test/dma-fix branch of sound GIT tree. git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6.git test/dma-fix
This basically adds dma_mmap_coherent() function to feasible architectures, which is already implemented for ARM, so far.
Cool - but needs a little further tweaking to work right. That's a solution which will use uncached accesses on all MIPS systems.
IP27/IP35-family machines will explode when you try that. Eventually the cache coherency logic will notice that cache, directory caches and memory have become inconsistent and bombard the CPU with a bunch of nasty exceptions.
For cache-coherent machines otoh it's a big waste of performance.
int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, dma_addr_t handle, size_t size) { struct page *pg;
if (!plat_device_is_coherent(dev)) vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); cpu_addr = (void *)dma_addr_to_virt(handle); pg = virt_to_page(cpu_addr);
return remap_pfn_range(vma, vma->vm_start, page_to_pfn(pg) + vma->vm_pgoff, size, vma->vm_page_prot); } EXPORT_SYMBOL(dma_mmap_coherent);
Thomas - you're the IP28 specialist. Would the plat_device_is_coherent() above have to become a cpu_is_noncoherent_r10000() call? Any further nasties?
Ralf