Re: [PATCH] ALSA: usb-audio: don't resubmit MIDI URBs at once on -EPIPE

[Takashi Iwai <tiwai@suse.de>]

On Thu, 29 Oct 2026 17:57:01 +0100,
Stjepan Poljak wrote:
> 
> When a USB MIDI device answers with a stall, as a bus-powered keyboard
> does while it is being switched off, snd_usbmidi_urb_error() falls
> through to the default case: it logs "urb status -32" and returns 0, so
> the completion handler resubmits the URB at once. That fails the same
> way, so the URBs loop, logging every failure, until the disconnect is
> processed.
> 
> On a Raspberry Pi 3B+ with a keyboard behind the onboard hub, that
> disconnect is never processed. Printing to the framebuffer and serial
> consoles holds the loop to about 250 messages a second, and all
> interrupts are handled on CPU 0, so the hub's port change isn't handled:
> the keyboard stays silent until it is replugged. With loglevel=3, the
> same kernel processes the disconnect 0.04-0.24 s after the first error
> and the keyboard works again.
> 
> Treat -EPIPE like the other errors seen while a device goes away: retry
> from the error timer after ERROR_DELAY_JIFFIES, without a message. An
> endpoint that is really halted wasn't cleared before either; it is now
> retried every 100 ms instead of continuously.
> 
> Tested on the Raspberry Pi 3B+ (rpi-6.12.y, dwc_otg) with the default
> console settings: after each off/on the disconnect is processed, the
> keyboard re-enumerates and plays, and nothing is logged for the stall.
> 
> Assisted-by: LLM
> Signed-off-by: Stjepan Poljak <stjepan.poljak@gmail.com>

This looks like a better solution, indeed.

Applied now.  Thanks.


Takashi