Re: Audio interface causing "xhci_hcd ... WARN: buffer overrun event" messages

[Robert Ham <rah@settrans.net>]

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On 31/07/2025 15:26, Mathias Nyman wrote:
> On 31.7.2025 13.11, Robert Ham wrote:
>> I managed to sort out the tracing and debug output. Updated kernel log
>> and trace:
>>
>> https://settrans.net/~rah/misc/xhci-kernel-log-2.txt
>>
>> https://settrans.net/~rah/misc/xhci-kernel-trace-2.txt
>>
>>
>> On 31/07/2025 09:27, Michał Pecio wrote:
>>
>>> Can you post "lsusb -v" for this device?
>>
> 
> Looks like The lengths and offsets in the URB, passed by audio driver does
> not match the transfer sizes the device reports it will send.
> 
> The audio device reports its isoc endpoint will send 1000 bytes
> every 125 microseconds:
> (from your lsusb)
> 
>>        Endpoint Descriptor:
>>          bLength                 7
>>          bDescriptorType         5
>>          bEndpointAddress     0x81  EP 1 IN
>>          bmAttributes           37
>>            Transfer Type            Isochronous
>>            Synch Type               Asynchronous
>>            Usage Type               Implicit feedback Data
>>          wMaxPacketSize     0x03e8  1x 1000 bytes
>>          bInterval               1
> 
> Trace shows xhci sets up the endpoint correctly,
> expecting 1000 bytes every 125 mictoseconds:
> 
> pulseaudio-1435    [000] .....    55.126749: xhci_ring_alloc: ISOC
> 00000000c42321b6: enq 0x00000002483a2000(0x00000002483a2000) deq
> 0x00000002483a2000(0x00000002483a2000) segs 2 stream 0 bounce 1000 cycle 1
> pulseaudio-1435    [000] .....    55.126750: xhci_add_endpoint: State
> disabled mult 1 max P. Streams 0 interval 125 us max ESIT payload 1000
> CErr 0 Type Isoc IN burst 0 maxp 1000 deq 00000002483a2001 avg trb len 1000
> 
> but the URB queued from class driver to xhci doesn't match this.
> Looks like one URB contains 8 isoc transfers, (one filled every 125us)
> but URB expects
> only 2880 bytes in total, leading to only 360 bytes per isoc transfer.
> 
> I'd take a closer look at the values filled by the audio driver to the
> struct usb_iso_packet_descriptor iso_frame_desc[] array, and
> number_of_packets
> in the URB

Thanks for your response, that's really helpful.

Cheers,

Bob


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