[QUESTION] ISA overhead

[QUESTION] ISA overhead

[BALBIR SINGH]

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With 2.5 coming soon, something about ISA has been bothering me.

All DMA has been limited to 16MB, this is ofcourse going to go
away with the PCI DMA patch which allows PCI-DMA to use all the
memory (4GB for 32 bit cards). All the setup of page-frames, etc
is done with the knowledge of ISA.

I was wondering if ISA should be treated as a special case in 2.5
and only if the ISA bus and/or ISA device is present should we do
the 16MB setup. Are there other devices (like MCA) limited to doing
16 MB or so of DMA?, if so they too should be handled as a special case.

I think this is the correct approach, now that all available devices
are almost PCI. The default DMA space should be 32 bit, with special
devices or buses like ISA being handled differently. The current code
should be hidden under a #ifdef and be enabled only if CONFIG_
ISA_DMA or something similar is set.

Comments, suggestions

Balbir

PS: Please do not worry about the attachment, I have no control over it.

"Accepting criticism is the fastest way to learn the right things"
- Just made it up (I am no longer scared of being flamed)



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Re: [QUESTION] ISA overhead

[Alan Cox]

> All DMA has been limited to 16MB, this is ofcourse going to go
> away with the PCI DMA patch which allows PCI-DMA to use all the

PCI DMA has always been for all the mapped memory