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Re: cache coherency in DMA and MMIO

From: Samuel Thibault
Subject: Re: cache coherency in DMA and MMIO
Date: Thu, 22 Apr 2010 17:01:50 +0200
User-agent: Mutt/1.5.12-2006-07-14

Samuel Thibault, le Thu 22 Apr 2010 16:51:38 +0200, a écrit :
> Da Zheng, le Thu 22 Apr 2010 22:37:51 +0800, a écrit :
> > So does the driver need to consider about cache coherency problems on PC 
> > when
> > interacting with the external device?
> Yes (since you can not rely on the BIOS), you need to remap the mmio
> range with cache disabled: INTEL_PTE_NCACHE|INTEL_PTE_WTHRU. This should
> already be done by pmap_enter().

And you need to access it using the volatile qualifier.


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