On Sun, Dec 6, 2009 at 12:13 AM, Roland Dreier <rol...@digitalvampire.org> wrote: > > Im not an expert on the ral driver, but openbsd drivers practically > > never map device registers into memory. The value of flags will be > > written to hardware later. > > Unless I'm misunderstanding the driver, the TX ring is in system > memory -- in other words the device will read the descriptors from > RAM, any time after they are written. There is an MMIO register to > kick the chip and ask it to start processing the TX ring, but I think > a sequence like the following is completely possible:
Oh, sorry, I somehow got stuck thinking you thought desc->flags was a register on the device. That would be unusual. Your explanation makes sense to me. Until somebody comes along to give the right answer :), I think normal practice is to call bus_dmamap_sync. It looks like most of the calls to setup_tx_desc are followed by a sync, but that wouldn't help order the writes within the call.
