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

Martyn Welch
2009-08-11T12:48:15Z

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.
>

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