Messages in this thread |  | | | Date | Tue, 11 Aug 2009 09:02:52 +0100 | | From | Martyn Welch <> | | Subject | Re: [patch 1/5] Staging: VME Framework for the Linux Kernel |
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Emilio G. Cota wrote: > 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 >
Buffer where? On VME or PCI, where are you transferring it to? The API I have will allow scattered locations on VME to be copied to PCI and visa-versa, scattered locations on PCI to be copied to VME and visa-versa. Even scattered locations on VME to scattered locations on PCI with a bit of effort.
> 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. >
But seems to fail to provide the flexibility that I outlined above.
Martyn > E. >
-- Martyn Welch MEng MPhil MIET (Principal Software Engineer) T:+44(0)1327322748 GE Fanuc Intelligent Platforms Ltd, |Registered in England and Wales Tove Valley Business Park, Towcester, |(3828642) at 100 Barbirolli Square, Northants, NN12 6PF, UK T:+44(0)1327359444 |Manchester,M2 3AB VAT:GB 927559189
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