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SubjectRe: Scatter-gather list constraints
Alan Stern wrote:
> On Mon, 23 Jun 2008, David Vrabel wrote:
>
>> Note that this 1024 byte multiple is for one particular WUSB mass
>> storage device. The WUSB standard permits max packet sizes of up 3584
>> (in multiples of 512), but I suspect WUSB mass storage devices will only
>> use 512, 1024, or 2048.
>>
>> For a solution, we may be able to do something if the HWA host
>> controller is passed a single URB with an s-g list (rather than one URB
>> per s-g list entry) and was careful about how it segmented the URB into
>> transfers to the rpipe.
>
> That would be ideal. However there is no way to pass an S-G list along
> with an URB; there's no field for it in the data structure. And none
> of the existing host controller drivers support such a thing.
>
> I suppose we could add a field to struct urb and add a flag indicating
> whether the controller driver supports S-G lists.

This is what I was thinking.

Can the number of entries in a sg list be limited? e.g., if the
hardware only had support for say, 64 entries?

David
--
David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562
Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/


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