Re: [Intel IOMMU][patch 4/8] Supporting Zero Length Reads in Intel IOMMU.

Andi Kleen
2007-04-24T19:30:07Z

On Tuesday 24 April 2007 08:03:03 Ashok Raj wrote:
> PCI specs permit zero length reads (ZLR) even if the mapping for that region
> is write only. Support for this feature is indicated by the presence of a bit
> in the DMAR capability. If a particular DMAR does not support this capability
> we map write-only regions as read-write.
>
> This option can also provides a workaround for some drivers that request
> a write-only mapping when they really should request a read-write.
> (We ran into one such case in eepro100.c in handling rx_ring_dma)

Better just fix the drivers instead of adding such hacks

-Andi