[PATCH 1/2] usb: dwc2: handle NAK when CHHLTD does not fire

[Sascha Hauer]

+Cc Chali Anis <chalianis1 at gmail.com>

On Mon, Apr 20, 2026 at 01:32:25PM +0200, Ahmad Fatoum wrote:
> Hello,
> 
> On 4/20/26 1:20 PM, Sascha Hauer wrote:
> > From: Sascha Hauer <sascha at saschahauer.de>
> > 
> > Some DWC2 configurations do not assert CHHLTD when a NAK is received;
> > the hardware keeps the channel active and only sets the NAK bit in HCINT.
> > wait_for_chhltd() polls for CHHLTD with a 10ms timeout; when CHHLTD never
> > fires the timeout expires and -ETIMEDOUT is returned without inspecting
> > HCINT. This causes the caller to treat the NAK as a hard error instead of
> > a retryable condition.
> > 
> > The symptom is that devices which NAK bulk or control transfers during
> > initialisation (e.g. some Samsung USB-C flash drives that NAK while their
> > firmware starts up) fail immediately rather than being retried via the
> > 5-second NAK-retry loop in dwc2_submit_bulk_msg() or the do/while loops
> > in dwc2_submit_control_msg().
> > 
> > Fix by reading HCINT before aborting the channel when the CHHLTD timeout
> > fires. If the NAK or FRMOVRUN bit is set, abort the channel, wait for the
> > abort to complete, and return -EAGAIN so that the existing retry logic can
> > handle the NAK. Log a diagnostic message if the channel abort itself times
> > out, which would indicate a real hardware problem.
> 
> How does this relate to
> https://lore.barebox.org/barebox/20260331034819.227094-1-chalianis1@gmail.com/
> 
> Do we need both? Only this one? Is there something over there, which you
> would want in your series?

Sounds related, but seems to be a different issue. It says "handle the case where
DMA has already completed by the time we get here". DMA is not an issue
in my case. We likely need a combination of both, but Chali, could you
give my patch without yours a try to see if it changes something for
good in your case?

Sascha

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