On Tue, 28 Nov 2006 08:04:40 -0800 (PST) "Amit S. Kale" <[EMAIL PROTECTED]> wrote:
> Hi Stephen, > > <SNIP> > > > > you need explicit bounce buffers. If you can't DMA from unaligned > address, > > > > > the write a small routine to copy the skb to a new one. > > > > > > > > > > > > The hardware supports DMA into 35 bit addresses. The intent is to > > > > enable DMA into addresses upto 32G. > > > > > > > > > > You should then set the same value for pci_set_dma_mask, because then > the IOMMU > > > can help. See both b44 or tg3 drivers, they have to deal with odd size > masks. > > > I don't think you have to do all the bounce buffer work in the driver. > > Using bounce buffers has following tradeoffs: > 1. Overhead of code maintenance. > 2. Slow performance. > Also on some ia64 machines we saw reduced performance because of larger > ring sizes. > > But if we remove bounce buffers and use IOMMU instead, it might not > work for some Opteron configurations. On one of our Opterons we could not > set the IOMMU from kernel command line (it asked to set it from the BIOS > where there was no > such option in the BIOS) > > So what do you suggest, should we use the IOMMU or should we keep the > bounce buffers as they are? > > Thanks, > Amit Kale. I don't mind workarounds, it is just that the problem is not unique to your driver and we need a platform or general solution. There are lots of devices that stupid hardware and need smaller masks. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
