Hi, "Yang, Fei" <fei.yang@xxxxxxxxx> writes: >>>>> Hey all, >>>>> I wanted to send these out for comment and thoughts. >>>>> >>>>> Since ~4.20, when the functionfs gadget enabled scatter-gather >>>>> support, we have seen problems with adb connections stalling and >>>>> stopping to function on hardware with dwc3 usb controllers. >>>>> Specifically, HiKey960, Dragonboard 845c, and Pixel3 devices. >>>> >>>> Any chance this: >>>> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git/commit/ >>>> ?h=testing/next&id=f63333e8e4fd63d8d8ae83b89d2c38cf21d64801 >>> This is a different issue. I have tried initializing num_sgs when debugging this adb stall problem, but it didn't help. >> >> So multiple folks have run through this problem, but not *one* has tracepoints collected from the issue? C'mon guys. Can someone, please, collect tracepoints so we can figure out what's actually going on? >> >> I'm pretty sure this should be solved at the DMA API level, just want to confirm. > > I have sent you the tracepoints long time ago. Also my analysis of the > problem (BTW, I don't think the tracepoints helped much). It's > basically a logic problem in function dwc3_gadget_ep_reclaim_trb_sg(). AFAICT, this is caused by DMA API merging pages together when map an sglist for DMA. While doing that, it does *not* move the SG_END flag which sg_is_last() checks. I consider that an overlook on the DMA API, wouldn't you? Why should DMA API users care if pages were merged or not while mapping the sglist? We have for_each_sg() and sg_is_last() for a reason. > I can try dig into my old emails and resend, but that is a bit hard to find. Don't bother, I'm still not convinced we should fix at the driver level when sg_is_last() should be working here, unless we should iterate over num_sgs instead of num_mapped_sgs, though I don't think that's the case since in that case we would have to chain buffers of size zero. -- balbi
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