linux-kernel - Re: [PATCH] usb: gadget: USB3 support to the legacy printer driver

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Message-ID: <20141119031049.GB24874@saruman>
Date:	Tue, 18 Nov 2014 21:10:49 -0600
From:	Felipe Balbi <balbi@...com>
To:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
CC:	"balbi@...com" <balbi@...com>,
	Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH]  usb: gadget: USB3 support to the legacy printer driver

On Tue, Nov 18, 2014 at 09:45:13PM +0000, Paul Zimmerman wrote:
> > From: linux-usb-owner@...r.kernel.org [mailto:linux-usb-owner@...r.kernel.org] On Behalf Of Felipe Balbi
> > Sent: Tuesday, November 18, 2014 12:47 PM
> > 
> > On Tue, Nov 18, 2014 at 03:41:43PM -0500, Jorge Ramirez-Ortiz wrote:
> > >
> > > notice that the original PLX driver was still far from the theoretical 5Gbps
> > > target (I was expecting to measure at least 3Gbps and could only get 1Gbps).
> > > So 1Gbps should be the target to meet on the kernel.org net2280 - do you agree?
> > 
> > this depends on a whole bunch of things. Mainline is a lot different
> > from PLX's kernel tree, I'm sure.
> > 
> > It also depends on how many PCIe lanes you're using. Just because USB3
> > guarantees 5Gbps bandwidth, if you use a 1x PCIe connector, you'll never
> > get that ;-)
> 
> Being pedantic, USB3 runs at 4Gbps, not 5Gbps. The signal transitions
> on the bus are at 5GT/s (5 giga-transitions per second), but due to the
> 8b/10b encoding, that equates to 4Gbps data rate.

I stand corrected :-)

-- 
balbi

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