Re: [PATCH v2] usbhid: tolerate intermittent errors

[Alan Stern <stern@rowland.harvard.edu>]

On Sat, Mar 07, 2026 at 07:57:09PM +0100, Liam Mitchell wrote:
> Modifies usbhid error handling to tolerate intermittent protocol
> errors, avoiding URB resubmission delay and device reset.
> 
> ---
> Protocol errors like EPROTO can occur randomly, sometimes frequently and are often not fixed by a device reset.
> 
> The current error handling will only resubmit the URB after at least 13ms delay and may reset the USB device if another error occurs 1-1.5s later, regardless of error type or count.
> 
> These delays and device resets increase the chance that input events will be missed and that users see symptoms like missed or sticky keyboard keys.
> 
> This patch allows one protocol error per 500ms to be tolerated and have the URB re-submitted immediately.
> 
> 500ms was chosen to be well above the error rate of a malfunctioning
> device but low enough to be useful for users with devices noisier than
> mine.
> 
> Signed-off-by: Liam Mitchell <mitchell.liam@gmail.com>
> Link: https://lore.kernel.org/linux-input/CAOQ1CL6Q+4GNy=kgisLzs0UBXFT3b02PG8t-0rPuW-Wf6NhQ6g@mail.gmail.com/
> ---

Liam, take a look at

	https://bugzilla.kernel.org/show_bug.cgi?id=221184

On Roman's system, these protocol errors occur fairly regularly, 
apparently caused by high system load.

Do you think a better approach might be to reduce the 13-ms delay to 
just 1 or 2 ms, and perform a reset only there has been no successful 
communication for about one second?  This might perhaps be _too_ lenient 
sometimes, but I don't think such situations will arise in practice.

The reason for having at least a small delay is to avoid getting into a 
tight resubmit/error loop in cases where the device has been unplugged.

Alan Stern