On Thu, Jan 29, 2009 at 10:57:13AM -0800, Matthew Dharm wrote: > On Thu, Jan 29, 2009 at 12:57:13PM -0500, Alan Stern wrote: > > On Thu, 29 Jan 2009, David Vrabel wrote: > > > > > Alan Stern wrote: > > > > > > > > Pushing scatterlists down to the HCD level would involve several > > > > nontrivial changes to the code. The issue of the buffer lengths is > > > > just one of them, although it is perhaps the most vexing. > > > > > > I don't see where the complexity is. The HCD simply fills the > > > hardware's s-g list structures based on the s-g list in the URB. > > > > I didn't say it was complex; I said it was nontrivial. That's because > > the existing HCD code is already complicated and difficult to decipher. > > > > > > > Obviously, none of the existing HCDs can support s-g lists in this > > > manner and should continue to only accept URBs without s-g lists. > > > > It's a little difficult to comprehend the intent behind this statement. > > Are you saying that if somebody does implement s-g lists for URBs, none > > of the existing HCDs should be changed to accept them? In that case, > > what use would they be? > > I think what he's saying (at least, what I read it to mean) was this: > Existing HCDs would use the existing mechanism for s-g lists. The new HCD > to support USB 3.0, which (apparently) has more capability, would process > the buffer list directly. The usb_sg_* code would need to be changed to > recognize a more capable HCD and pass the s-g list to that HCD for "direct" > processing. That was my idea when I was looking at sg-list support for xHCI. I just modified the usb_sg_* code to pass down the s-g list to the HCD if the HCD driver had the HCD_USB3 flag. This could be generalized to a HCD flag like HCD_SG_LIST if wireless host controllers want to support processing s-g lists. Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
