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From: David Laight <David.Laight@ACULAB.COM>
To: 'Johan Hovold' <johan@kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Antoine Aubert <a.aubert@overkiz.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] USB: serial: ftdi_sio: fix extreme low-latency setting
Date: Wed, 25 Jan 2017 15:19:31 +0000	[thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6DB026DF75@AcuExch.aculab.com> (raw)
In-Reply-To: <20170125143520.10982-1-johan@kernel.org>

From: Johan Hovold
> Sent: 25 January 2017 14:35
> Since commit 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY
> flag") the FTDI driver has been using a receive latency-timer value of
> 1 ms instead of the device default of 16 ms.
> 
> The latency timer is used to periodically empty a non-full receive
> buffer, but a status header is always sent when the timer expires
> including when the buffer is empty. This means that a two-byte bulk
> message is received every millisecond also for an otherwise idle port as
> long as it is open.
...

I'd wondered what all those packets were.
It seems beyond stupid that the hardware is sending them at all.

	David


      parent reply	other threads:[~2017-01-25 15:42 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-25 14:35 [PATCH] USB: serial: ftdi_sio: fix extreme low-latency setting Johan Hovold
2017-01-25 15:06 ` Greg Kroah-Hartman
2017-01-25 15:14   ` Johan Hovold
2017-01-25 15:42     ` Greg Kroah-Hartman
2017-01-25 16:02       ` Johan Hovold
2017-01-25 15:19 ` David Laight [this message]

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