On Friday, May 30, 2014 10:54:06 am Attilio Rao wrote: > On Tue, May 27, 2014 at 11:31 PM, Scott Long <sco...@freebsd.org> wrote: > > Author: scottl > > Date: Tue May 27 21:31:11 2014 > > New Revision: 266775 > > URL: http://svnweb.freebsd.org/changeset/base/266775 > > > > Log: > > Eliminate the fake contig_dmamap and replace it with a new flag, > > BUS_DMA_KMEM_ALLOC. They serve the same purpose, but using the flag > > means that the map can be NULL again, which in turn enables significant > > optimizations for the common case of no bouncing. > > While I think this is in general a good idea, unfortunately our > drivers do so many dumb things when freeing DMA allocated buffers that > having a NULL map is going to cause some "turbolence" and make such > bugs more visible. > An example is with ATA, where I think this fix is needed: > http://www.freebsd.org/~attilio/dmamem_free-ata.patch > > Otherwise, what can happen with bounce buffers, is that the allocated > memory via contig malloc was not going to be freed anytime. > > I tried to look around and I found questionable (read broken) code in > basically every driver which allocates DMA buffers, so I really don't > feel I want to fix the majority of our drivers. I just think such > paths are not excercised enough to be seen in practice often or the > bugs just get unnoticed.
Eh, many maps for static allocations were already NULL and have been for a long time. This is nothign new. Plus, the diff you posted has a bug regardless of explicitly destroying a map created by bus_dmamem_alloc(). -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
