On Wednesday, August 22, 2012 6:48:50 pm Oleksandr Tymoshenko wrote: > Author: gonzo > Date: Wed Aug 22 22:48:50 2012 > New Revision: 239597 > URL: http://svn.freebsd.org/changeset/base/239597 > > Log: > Do not change "cachable" attribute for DMA memory allocated with > BUS_DMA_COHERENT attribute > > The minimum unit for changing "cachable" attribute is page, so call > to pmap_change_attr effectively disable cache for all pages that newly > allocated DMA memory region spans on. The problem is that general-purpose > memory could reside on these pages too and disabling cache might affect > performance. Moreover ldrex/strex operators raise Data Abort exception > when accessing memory on page with "cachable" attribute off. > > BUS_DMA_COHERENT does nto require memory to be coherent. It just suggests > to do best effort for reducing synchronization overhead.
Alternatively you could force an allocation with BUS_DMA_COHERENT to always allocate at least one page. Also, it is probably better to match what I recently did in x86 and use kmem_alloc_contig() or kmem_alloc_attr() for allocations with a custom memory attribute rather than using pmap_change_attr() directly. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
