Re: alpha iommu fixes
Jonathan Lundell (jlundell@pobox.com)
Mon, 21 May 2001 06:55:29 -0700
At 3:19 AM -0700 2001-05-21, David S. Miller wrote:
>This is totally wrong in two ways.
>
>Let me fix this, the IOMMU on these machines is per PCI bus, so this
>figure should be drastically lower.
>
>Electrically (someone correct me, I'm probably wrong) PCI is limited
>to 6 physical plug-in slots I believe, let's say it's 8 to choose an
>arbitrary larger number to be safe.
>
>Then we have:
>
>max bytes per bttv: max_gbuffers * max_gbufsize
> 64 * 0x208000 == 133.12MB
>
>133.12MB * 8 PCI slots == ~1.06 GB
>
>Which is still only half of the total IOMMU space available per
>controller.
8 slots (and you're right, 6 is a practical upper limit, fewer for
66 MHz) *per bus*. Buses can proliferate like crazy, so the slot
limit becomes largely irrelevant. A typical quad Ethernet card, for
example (and this is true for many/most multiple-device cards), has a
bridge, its own internal PCI bus, and four "slots" ("devices" in PCI
terminology).
--
/Jonathan Lundell.
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