Re: MMIO and gcc re-ordering issue

Scott Wood
2008-05-27T18:33:23Z

Trent Piepho wrote:
> Is there an issue with anything _besides_ coherent DMA?
>
> Could one have a special version of the accessors for drivers that
> want to assume they are strictly ordered vs coherent DMA memory?
> That would be much easier to get right, without slowing _everything_
> down.

It's better to be safe by default and then optimize the fast paths than
to be relaxed by default and hang the machine in some piece of code that
runs once a month. "Premature optimization is the root of all evil",
and what not.

> One could even go as far as to allow a driver to "#define
> WANT_STRICT_IO" and then it would get the strict versions. Add that
> to any driver that uses DMA and then worry about vetting those
> drivers.

See above -- if you must have a #define, then it should be WANT_RELAXED_IO.

-Scott