Tejun Heo <htejun@xxxxxxxxx> wrote: > George Spelvin wrote: >> Tejun Heo <htejun@xxxxxxxxx> wrote: >>>> Q: Does the fact that I'm using the GART IOMMU mean that I'm not really using >>>> using 64-bit DMA at all? >>> Can you turn it off and see what happens? >> >> I can if I can verify that every other bus-master PCI device in the >> system can do 64-bit DMA. >> >> Do you know how to check that? I haven't found a file under /sys or >> /proc that tells me what the DMA masks are of various system >> drivers, but that doesn't mean that it doesn't exist. > > It doesn't really matter. The kernel will bounce buffers as > necessary. Er, according to the docs I can find, that's iommu=soft, and still doesn't guarantee 64-bit DMA. I was thinking about using iommu=off, which disables everything including bounce buffers, and thereby forces 64-bit DMA. Um... actually, I just tried it, and when there's >4G of memory, the kernel forces iommu=soft, and it works. At least as far as e2fsck -n on every file system (including a 1.7 TB RAID-5) can tell. It still doesn't definitively tell me that a DMA to and from an address >4G was done, but it's an awfully strong hint. I was thinking of inserting a debug message that logs every time the "highest DMA address used" increases, than I can watch it to see for sure. ATM I'm just recompiling the kernel from -rc6 to -rc7. It's in single-user mode so I can't ssh over the boot messages, but they definitely included "64bit" from ahci_print_info(). Speaking of anci_print_info(), sould something like the following be a good thing? diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c index 2e1a7cb..18137d2 100644 --- a/drivers/ata/ahci.c +++ b/drivers/ata/ahci.c @@ -2464,22 +2464,22 @@ static void ahci_print_info(struct ata_host *host) "%s\n" , - cap & (1 << 31) ? "64bit " : "", - cap & (1 << 30) ? "ncq " : "", - cap & (1 << 29) ? "sntf " : "", - cap & (1 << 28) ? "ilck " : "", - cap & (1 << 27) ? "stag " : "", - cap & (1 << 26) ? "pm " : "", - cap & (1 << 25) ? "led " : "", - - cap & (1 << 24) ? "clo " : "", - cap & (1 << 19) ? "nz " : "", - cap & (1 << 18) ? "only " : "", - cap & (1 << 17) ? "pmp " : "", - cap & (1 << 15) ? "pio " : "", - cap & (1 << 14) ? "slum " : "", - cap & (1 << 13) ? "part " : "", - cap & (1 << 6) ? "ems ": "" + cap & HOST_CAP_64 ? "64bit " : "", + cap & HOST_CAP_NCQ ? "ncq " : "", + cap & HOST_CAP_SNTF ? "sntf " : "", + cap & (1 << 28) ? "ilck " : "", + cap & HOST_CAP_SSS ? "stag " : "", + cap & HOST_CAP_ALPM ? "pm " : "", + cap & (1 << 25) ? "led " : "", + + cap & HOST_CAP_CLO ? "clo " : "", + cap & (1 << 19) ? "nz " : "", + cap & (1 << 18) ? "only " : "", + cap & HOST_CAP_PMP ? "pmp " : "", + cap & (1 << 15) ? "pio " : "", + cap & HOST_CAP_SSC ? "slum " : "", + cap & (1 << 13) ? "part " : "", + cap & HOST_CAP_EMS ? "ems ": "" ); } -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
