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

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Date:	Tue, 18 Nov 2014 14:47:08 -0600
From:	Felipe Balbi <balbi@...com>
To:	Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
CC:	<balbi@...com>, Greg KH <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH]  usb: gadget: USB3 support to the legacy printer driver

Hi,

On Tue, Nov 18, 2014 at 03:41:43PM -0500, Jorge Ramirez-Ortiz wrote:
> >>> you have no clue what these mean, do you ? How about reading the USB
> >>> specification of even http://www.beyondlogic.org/usbnutshell/usb1.shtml
> >>
> >> Unfortunately I do.
> >> It was easier to temporarily hack the driver code for a test - while I
> >> was at it - rather than modifying the host code.
> >> Since you asked for them, I though you would read the logs and wonder
> >> where the funny ids where coming from.
> > why do you even need to hack the host driver for these ? The driver
> > shows a Printer Class interface and the linux host side driver should
> > bind to it without any issues.
> 
> the hack was on the gadget side.
> 
> the usbhost test code in charge of sending the file to the device had the wrong ids.
> to save time -since I was modifying the gadget driver code and only for the
> tests (it is not part of the final patch) - I hacked those ids on the printer.c
> file.
> but anyway. lets move on. I removed those, recompiled the usb host code and sent
> the new traces.

then the host side needs a fix because it shouldn't really care about
the device ID, rather it should care about the class being printer.

> >> That hack above would have given you an answer: so I kind of know what
> >> the ids are for. honestly.  anyway, will send the new logs - it took
> >> me a while to find and modify the host test code.
> > Which host test code ? Why don't you just use lpr or even cat file >
> > /dev/lp0 or something like that ?
> 
> it is some proprietary code that links libusb -part of a different project: it
> was useful as it generated some metrics I was interested in.

I would be surprised if lpr doesn't work for the same purpose.

> >>> do you want to debug that and find the culprit since you're already at
> >>> it ?
> >> probably: I still need to get used to this process, thanks for bearing
> >> with me on this.
> > no problem.
> >
> >> I spoke to Ricardo Ribalda three months ago while I was doing this
> >> stuff.  but yes, I might work on this -after I finish with this
> >> patch!- since I have access to the hardware locally.
> > cool, that'll help.
> 
> 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 ;-)

-- 
balbi

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