Re: [PATCH] usb: chipidea: udc: give up when the endpoint halt bit is not taken

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] usb: chipidea: udc: missing Fixes trailer for hw_ep_set_halt()
  hang fix
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commit a303d4e574823163c056eaedbfb37d82c4fbaacb
Author: Mario Behn <mario.behn@gmail.com>

> usb: chipidea: udc: give up when the endpoint halt bit is not taken
>
> hw_ep_set_halt() writes the stall bit of an endpoint and loops until it
> reads back. On endpoint 0 the controller clears the stall bit itself when
> a SETUP packet arrives, so when one arrives while the driver stalls the
> endpoint the loop never ends. It runs in the UDC interrupt thread with the
> controller lock held, and the SETUP packet it is waiting out can only be
> consumed by that same thread.
>
> Seen on a Zynq-7000 (an ADALM-PLUTO class board, PREEMPT_RT) during the
> host RNDIS initialisation: the gadget stalls the GET_ENCAPSULATED_RESPONSE
> poll that has no answer yet, the stall is refused, the interrupt thread
> spins for a minute, RCU stalls and every other USB operation blocks on the
> lock. With a bounded loop the condition shows on 1 to 3 percent of boots
> and is harmless: the pending SETUP packet is handled next and the host
> repeats its poll.
>
> Retry for about a millisecond, then warn with the endpoint control and
> setup status registers and return -EBUSY. The callers already report a
> failed stall.
>
> A loop timeout for the same hang was proposed in 2021 (usb: chipidea: add
> loop timeout for hw_ep_set_halt(), Jeaho Hwang) and not applied.
>
> Signed-off-by: Mario Behn <mario.behn@gmail.com>

[Severity: Low]
This fixes the unbounded polling loop in hw_ep_set_halt() introduced with the
initial driver.  Should this include:

  Fixes: aa69a8093ff9 ("USB: gadget: MIPS ci13xxx_udc")

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Sashiko AI review · https://sashiko.dev/#/patchset/20261105205343.982465-1-mario.behn@gmail.com?part=1