On Tue, 02 Mar 2010 05:55:34 -0800 (PST) David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > Date: Tue, 2 Mar 2010 14:54:11 +0100 > > > Broken in the sense that arch/powerpc/Kconfig describes CONFIG_IOMMU_VMERGE: > > > > Cause IO segments sent to a device for DMA to be merged virtually > > by the IOMMU when they happen to have been allocated contiguously. > > This doesn't add pressure to the IOMMU allocator. However, some > > drivers don't support getting large merged segments coming back > > from *_map_sg(). > > > > Most drivers don't have this problem; it is safe to say Y here. > > > > I don't know if this comment still applies to any drivers in the mainline > > kernel, but it's possible. > > That really has to be out of date these days. Yeah, I think so. I added dma_get_max_seg_size() several years ago so that device drives can tell IOMMU about the maximum segment length that they can handle. And the default limit (64K) should work for everyone, I think. I guess that the comment was written when IOMMU was able to merge as many segments as possible with ignoring the device limitation. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
