On Wed, Jun 21, 2017 at 05:37:22PM +0200, Joerg Roedel wrote: > > Do you mean this is like the last exception case in that document above: > > > > " > > - Pointers to data structures in coherent memory which might be modified > > by I/O devices can, sometimes, legitimately be volatile. A ring buffer > > used by a network adapter, where that adapter changes pointers to > > indicate which descriptors have been processed, is an example of this > > type of situation." > > > > ? > > So currently (without this patch) the build_completion_wait function > does not take a volatile parameter, only wait_on_sem() does. > > Wait_on_sem() needs it because its purpose is to poll a memory location > which is changed by the iommu-hardware when its done with command > processing. Right, the reason above - memory modifiable by an IO device. You could add a comment there explaining the need for the volatile. > But the 'volatile' in build_completion_wait() looks unnecessary, because > the function does not poll the memory location. It only uses the > pointer, converts it to a physical address and writes it to the command > to be queued. Ok. Thanks. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html