Re: MMIO and gcc re-ordering issue

Roland Dreier
2008-05-27T17:48:51Z

> Actually, this specifically should not be. The need for mmiowb on altix
> is because it explicitly violates some of the PCI rules that would
> otherwise impede performance. The compromise is that readX on altix
> contains the needed dma flush but there's a variant operator,
> readX_relaxed that doesn't (for drivers that know what they're doing).
> The altix critical drivers have all been converted to use the relaxed
> form for performance, and the unconverted ones should all operate just
> fine (albeit potentially more slowly).

Is this a recent change? Because as of October 2007, 76d7cc03
("IB/mthca: Use mmiowb() to avoid firmware commands getting jumbled up")
was needed. But this was involving writel() (__raw_writel() actually,
looking at the code), not readl(). But writel_relaxed() doesn't exist
(and doesn't make sense).

- R.