[patch 1/5] Staging: VME Framework for the Linux Kernel

Emilio G. Cota cota at braap.org
Mon Aug 10 19:50:48 UTC 2009

Martyn Welch wrote:
> If the driver writer wants a "single shot" effect, there's little  
> overhead in creating a one item link-list and executing it. However,  
> without support for this mode the author is stuck with single shot  
> transfers.  If the author wants to perform scatter gather type  
> transfers, without this functionality in the API - which is supported by  
> all the bridges I have seen - he won't be able to easily avail himself  
> of this functionality and get "work done".

Again, he (the driver writer) should know *nothing* about that.

As for the scatter-gather case, what should happen is:

User:		hey, there's a buffer I want to transfer. here's
		a pointer and size
VME layer:	ok, passing it to the bridge
VME bridge:	I know I'm over PCI, so I'll get the pages
		from memory and map the sg list over PCI, and
		then will tell the bridge to perform from there.

That's just a particular example, but for the user (read driver
writer) it's much simpler this way. Doesn't need to know about
lists or whatever.


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