RE: [PATCH v3 1/2] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers

[Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)]

Hi Johan,  

Understood. I will drop this patch. Thanks for the review.  

Regards,
Navee

-----Original Message-----
From: Johan Hovold <johan@xxxxxxxxxx> 
Sent: Tuesday, 21 July 2026 3:34 pm
To: Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG) <naveen.reddy@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Arun Pappan (FTDI-SG) <arun.pappan@xxxxxxxxxxxx>
Subject: Re: [PATCH v3 1/2] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers

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On Tue, Jun 23, 2026 at 04:03:20PM +0800, Chinna Mopurigari Naveen Kumar Reddy wrote:
> usb_control_msg() can return -ETIMEDOUT, -EPIPE or -EPROTO on a
> functioning device when the host controller is momentarily unable to
> complete the transfer.  These are transient conditions that surface
> under heavy USB bus load -- for example when several high-baud FTDI
> channels share a busy host controller -- and a short retry generally
> succeeds.

As you described here in v1 of this patch you observed this with an
out-of-tree host controller driver where this is just one symptom.

So this falls in the same category of random function driver workarounds
for what are really host controller driver issues.

Just configure your latency timers before overloading the controller, or
have your userspace retry on errors.

Johan