On Mon, Jan 09, 2012 at 04:31:59PM +0100, Sebastian Andrzej Siewior wrote: > On 01/09/2012 04:09 PM, Greg KH wrote: > >On Mon, Jan 09, 2012 at 03:32:38PM +0100, Sebastian Andrzej Siewior wrote: > >>On 01/09/2012 03:23 PM, Matthew Wilcox wrote: > >>>On Mon, Jan 09, 2012 at 01:55:02PM +0100, Sebastian Andrzej Siewior wrote: > >>>>Hi Sarah, > >>>> > >>>>I've been looking into UAS support for hcds without support for sg. > >>> > >>>I think that's fundamentally the wrong approach. Instead, HCDs should > >>>be modified to add support for SGs. I posted a patch series that made > >>>progress towards that goal a while back. > >> > >>That is what Felipe and I decided for the gadget framework. > >>Alan / Greg, any comments from your side? > > > >HGs should be supporting sg, why are they not? > > It was not required in the first place because it was added later to > the usb framework. The EHCI, WHCI and XHCI host driver are the only > supporting it. I posted patches for dummy_hcd so we have 4 which > support it. There is a total of 22 hcds which makes 18% which have it > implemented. Ok, and why would you want to run a UAS device on anything other than those controllers? > usb_sg_init() provides a workaround for them. So if the HCD supports sg > it ends up with one URB. If it does not the function allocates a bunch > of URBs and sets urb->transfer_buffer = sg_virt(sg) for each sg entry > which should work. It will fail if the hcd supports DMA transfers (no > bounce buffer from the scsi host because it can handle high mem) and > does not support sg (for the HIGHMEM page the transfer_buffer will be > set to NULL). > So that could be one problem we have. > UAS is not using this function. It comes with usb_sg_wait() which > queues the URBs _and_ waits until the transfer is complete. For UAS > it should be non-blocking because we need to do this from IRQ > context. > > So the question is how to deal with it. Fix the UAS driver to not do a blocking call from interrupt context? greg k-h -- 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
