[patch 1/5] Staging: VME Framework for the Linux Kernel
Emilio G. Cota
cota at braap.org
Mon Aug 10 12:50:48 PDT 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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