Andy Shevchenko <[email protected]> writes: > On Wed, Nov 11, 2015 at 1:07 AM, Måns Rullgård <[email protected]> wrote: >> Andy Shevchenko <[email protected]> writes: > >>>>>> + nb8800_writel(priv, NB8800_TX_DESC_ADDR, txb->dma_desc); >>>>>> + wmb(); /* ensure desc addr is written before starting >>>>>> DMA */ >>>>> >>>>> Hm… Have I missed corresponding rmb() ? If it's about MMIO, perhaps >>>>> mmiowb() ? >>>> >>>> Possibly. >>> >>> Standalone wmb() doesn't make sense. >> >> It does if you need to enforce ordering between normal and I/O memory. >> In fact, since the descriptor is filled in using normal memory accesses, >> my understanding is that mmiowb() would be insufficient here. The >> comment could be improved, however. > > Can you then explain what exactly you are assured against in all cases > where you are using wmb()s? It seems I don't recognize this part in > some excerpts.
Certainly. I'll re-read memory-barriers.txt to make sure I'm doing the right thing, then write a better comment. -- Måns Rullgård [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
