Re: [PATCH 1/2] usbcore: Add quirk for 255-bytes initial config read

[Michal Pecio]

On Mon, 27 Jul 2026 20:55:27 +0530, Nikhil Solanke wrote:
> Regarding the "stall" wording, I was referring to the condition where
> they fail with -EPIPE error when these devices are connected through
> external usb hubs. The directly connected devices I've tested
> typically fail with -EPROTO instead.  I'm happy to reword the comment
> if you think that would make it clearer.

Understood.

The reason you see -EPIPE is due to the marvel of technology which is
"transaction translators" in USB 2.0 hubs. They report low/full-speed
protocol errors with STALL handshake on the high-speed bus, even though
a new ERR handshake is also defined and used for similar errors on
interrupt endpoints only.

So your device doesn't stall, it just disconnects as usual. And with
a USB 1.0 hub you would see -EPROTO too, but these are rare today.


My habit is to make code comments generic - I don't know what devices
will use this quirk in the future, so just write something that likely
applies to all of them - "break", "malfunction", "fail to respond".
But I also describe precisely what problem the quirk was meant to solve
in the commit, so the information can be found with "git blame".

Regards,
Michal