[PATCH] mpt2sas: Fall back to 64 bit coherent mask if 64 bit DMA / 32 bit coherent mask not supported

Arnd Bergmann arnd at arndb.de
Wed May 13 18:10:50 AEST 2015

On Tuesday 12 May 2015 18:24:43 Brian King wrote:
> Commit 5fb1bf8aaa832e1e9ca3198de7bbecb8eff7db9c broke 64 bit DMA for mpt2sas on Power.
> That commit changed the sequence for setting up the DMA and coherent DMA masks so
> that during initialization the driver requests a 64 bit DMA mask and a 32 bit consistent
> DMA mask, then later requests a 64 bit consistent DMA mask. The Power architecture does
> not currently support this, which results in always falling back to a 32 bit DMA window,
> which has a negative impact on performance. Tweak this algorithm slightly so that
> if requesting a 32 bit consistent mask fails after we've successfully set a 64 bit
> DMA mask, just try to get a 64 bit consistent mask. This should preserve existing
> behavior on platforms that support mixed mask setting and restore previous functionality
> to those that do not.
> Signed-off-by: Brian King <brking at linux.vnet.ibm.com>

I believe the way the API is designed, it should guarantee that after dma_set_mask()
succeeds for a device, dma_set_coherent_mask() with the same mask will also succeed.

Could you just call dma_set_mask_and_coherent() here to avoid that complex logic?


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