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

[Russell King - ARM Linux Admin]

Philip Blundell writes:
> I've never been convinced that the hard dichotomy between "host" and "plug-in" 
> mode is necessary or desirable.  But this point of view seemed rather 
> unpopular last time I aired the idea.

It is not desirable for the following reasons:

1. Linux will assign addresses to any non-setup peripheral,
   potentially causing havoc with the PCs setup of the PCI
   bus.  It is not for Linux to play with the configuration
   registers in add-in mode, but for host mode it must do.
   (generic code).
2. virt_to_bus is heavily dependent on the mapping of the
   memory to the PCI bus.  The BIOS sets the base address
   of the EBSA285's memory on the PCI bus.  It is again
   not for Linux to second-guess the BIOS, nor the PNP bios
   in the host PC.  Since virt_to_bus and friends are
   referenced many times, I feel that it is not desirable
   to slow down the kernel (possibly considerably) by having
   to calculate non-constant offsets for the virtual to PCI
   mapping.

> You will need to find a way for the EBSA-285 to see the
> right interrupt numbers.  This is going to be hardware
> dependent and in some cases it may not even be possible
> -- if the IDE interface is built in to your motherboard 
> chipset it may not be capable of generating interrupts
> on the PCI bus.

Probably won't be capable, and what a good argument against
combining host and add-in mode.  Host and add-in mode are
two completely separate beasts.

> With a plugin card you will stand more of a chance.

No.  With a host card you stand more of a chance of getting
the interrupts.
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