Messages in this thread | | | Date | Mon, 23 Jun 2008 20:06:52 +0100 | From | David Vrabel <> | Subject | Re: Scatter-gather list constraints |
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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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