MMIO and gcc re-ordering issue
rdreier at cisco.com
Wed May 28 03:38:56 EST 2008
> 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).
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