On Mon, 2011-09-26 at 15:51 -0700, Sarah Sharp wrote: > Hi Andiry, > > I dug the original branch out of my tree from when I started the dynamic > ring expansion code. I've stuck it up on github, since kernel.org is > still down: > > https://github.com/sarahsharp/xhci/tree/xhci-ring-expansion-simplified > > You might find something helpful in there. I'm not too attached to that > code in particular over anything new you create, but I was trying to > remember the pitfalls I ran into when I started coding the dynamic ring > expansion. Looking at the patches I started out with (`git diff > 7d6d62f^..e109a04), I notice a couple things: > Oh, I don't realize that you've been working on it over a year ago. I'll check that code first. > 1. My patchset is pretty careful about what it does with the toggle > cycle bit. Does your patchset handle that properly when you > concatenate the two rings, or does it leave the toggle cycle bit set > in the last link TRB of the original ring, so you have the toggle > cycle bit set twice in a ring? > Yes, the cycle bit must be treated very carefully. I think the TC bit should be only set in the last segment of a ring, so I made patch2 which is used to allocate new segments with the same cycle bit setting as the old ring. > 2. You need to let drivers know how many scatter-gather list entries > they can post in one URB. The USB storage driver in particular > uses this to queue larger data phases of SCSI commands. You can do > that by setting hcd->self.sg_tablesize to 0 (meaning "unlimited" > entries). > > 3. Apparently I also needed to increase the .max_sectors > variable in the USB storage driver to get bigger scatter-gather > transfers. I think that would have to be a separate patch to the > usb-storage list, but it might help you test your patchset with a > non-isochronous device (and one that might use different sized > transfers and exercise ring expansion at different times). > > Let me know if you have any other questions. Thanks for looking into > writing the code for dynamic ring expansion. :) > Apparently the ring expansion is much more complicated than I thought. Thanks for the elaborate explanation! It's really appreciated and helpful. I will re-consider the whole logic. I did this just for fun and thought it may be helpful to you. Thanks, Andiry -- 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
