Re: EBSA285 in Add-in Mode + Local ide disk

[Russell King - ARM Linux Admin]

Gaixia Zhang writes:
> Has anybody ever tried to run EBSA285 in Add-in Mode and access
> the PC PCI-ide drive as a local disk? Is it possible? I mean to let
> EBSA285 access the disk directly other than through NFS as Mark did?

I wouldn't have thought so.  In order to use IDE with Linux, you need
an interrupt.  The PCI southbridges (which contain the IDE interface
on PCs) which I have come across internally route the IDE interrupt
to the interrupt controller (also in the Southbridge), which means
that it never appears on the PCI bus.

This means that Linux on an add-in EBSA285 in a PC will never be able
to see the interrupt, and therefore will not be able to function.

Yes, you could write your own IDE driver that didn't rely on interrupts,
but the performance would be so dire to make it undesirable.

There is a falicy persistently introduced by Phil into his patches
(against my judgement) which will bite hard with the later 2.3
kernels.  He allows you to configure a host EBSA to be used in plug-in
mode.  This is 100% bad if you're using a PNP BIOS with a PNP OS,
since the EBSA285 will set your PCI bus up for you, possibly even
before the PC's BIOS has looked at it.  The result could be all
hell breaking loose when the OS starts on the host, or when the
BIOS refiddles the PCI bus.  My many complaints did nothing, so
people using his "development" patches do so at their own (potentially
disasterous) risk.
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