From: Johan Hovold <johan@kernel.org>
To: Chinna Mopurigari Naveen Kumar Reddy <naveen.reddy@ftdichip.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
Arun Pappan <arun.pappan@ftdichip.com>
Subject: Re: [PATCH v3 1/2] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers
Date: Tue, 21 Jul 2026 09:33:32 +0200 [thread overview]
Message-ID: <al8gzIupMhXqWq9u@hovoldconsulting.com> (raw)
In-Reply-To: <37cc6844010da737aeae61e0248fb3e9ca5e35b0.1782201674.git.naveen.reddy@ftdichip.com>
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
next prev parent reply other threads:[~2026-07-21 7:33 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-22 7:38 [PATCH 0/6] USB: serial: ftdi_sio: configurable read-URB defer, per-port low_latency, latency_timer reliability Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 7:38 ` [PATCH 1/6] USB: serial: ftdi_sio: add configurable inter-batch defer for read URBs Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 8:51 ` Greg Kroah-Hartman
2026-06-22 8:52 ` Greg Kroah-Hartman
2026-06-22 9:05 ` Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
2026-06-22 9:27 ` Greg Kroah-Hartman
2026-06-22 9:43 ` Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
2026-06-22 7:38 ` [PATCH 2/6] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 7:38 ` [PATCH 3/6] USB: serial: ftdi_sio: make explicit latency_timer sysfs write authoritative Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 7:38 ` [PATCH 4/6] USB: serial: ftdi_sio: add per-port low_latency sysfs attribute Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 7:38 ` [PATCH 5/6] USB: serial: ftdi_sio: serialise low_latency toggle against read_bulk_callback Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 7:38 ` [PATCH 6/6] USB: serial: ftdi_sio: pace low_latency ports with low_latency_defer_ns Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 9:43 ` [PATCH v2 0/2] USB: serial: ftdi_sio: latency_timer reliability fixes Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 9:43 ` [PATCH v2 1/2] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 9:43 ` [PATCH v2 2/2] USB: serial: ftdi_sio: make explicit latency_timer sysfs write authoritative Chinna Mopurigari Naveen Kumar Reddy
2026-06-22 10:19 ` Greg Kroah-Hartman
2026-06-23 0:20 ` Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
2026-06-23 8:03 ` [PATCH v3 0/2] USB: serial: ftdi_sio: latency_timer reliability fixes Chinna Mopurigari Naveen Kumar Reddy
2026-06-23 8:03 ` [PATCH v3 1/2] USB: serial: ftdi_sio: retry transient errors on chip-side control transfers Chinna Mopurigari Naveen Kumar Reddy
2026-07-21 7:33 ` Johan Hovold [this message]
2026-07-21 7:45 ` Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
2026-06-23 8:03 ` [PATCH v3 2/2] USB: serial: ftdi_sio: make explicit latency_timer sysfs write authoritative Chinna Mopurigari Naveen Kumar Reddy
2026-07-21 8:03 ` Johan Hovold
2026-07-22 5:29 ` Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
2026-07-17 6:39 ` [PATCH v3 0/2] USB: serial: ftdi_sio: latency_timer reliability fixes Chinna Mopurigari Naveen Kumar Reddy (FTDI-SG)
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