Hello Hans, On 15.03.2015 17:26, Hans Verkuil wrote: > On 03/12/2015 08:37 PM, Florian Echtler wrote: >> On 09.03.2015 15:02, Hans Verkuil wrote: >>> On 03/09/2015 02:45 PM, Florian Echtler wrote: >>>> On 09.03.2015 11:09, Hans Verkuil wrote: >>>>> The error almost certainly comes from usb_submit_urb(). That function does some >>>>> checks on the sgl: >>>>> >>>> I'll do my best to track this down. Do you think this is an error in my >>>> code, one in the USB subsystem, or some combination of both? >>> >>> If the USB core indeed requires scatter-gather segments of specific lengths >>> (modulo max), then that explains the problems. >>> So as suggested try to see if the usb core bails out in that check and what the >>> 'max' value is. It looks like only XHCI allows SG segments of any size, so I really >>> suspect that's the problem. But I also need to know the 'max' value to fully >>> understand the implications. >> >> Finally managed to confirm your suspicions on a kernel with a patched >> dev_err call at the location you mentioned: >> >> So the SG segments are expected in multiples of 512 bytes. I assume this >> is not something I can fix from within my driver? > > No, you can't. I would use dma-sg, but disable the USERPTR support. > Also comment why USERPTR support is disabled. > > This was interesting :-) > Thanks again for your help, new patch is submitted. Just for my understanding: is this a hardware limitation? And why does dma-sg select such a weird segment size like 4080? Best, Florian -- SENT FROM MY DEC VT50 TERMINAL
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