linux-kernel - Re: [PATCH 1/3] usb: udc: Fix gadget driver's speed check in various UDC drivers

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Date:	Sat, 19 Nov 2011 16:02:24 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Michal Nazarewicz <mpn@...gle.com>
cc:	Greg Kroah-Hartman <gregkh@...e.de>, Felipe Balbi <balbi@...com>,
	Thomas Dahlmann <dahlmann.thomas@...or.de>,
	Anton Vorontsov <avorontsov@...mvista.com>,
	Anatolij Gustschin <agust@...x.de>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Ben Dooks <ben@...tec.co.uk>, Heiko Stubner <heiko@...ech.de>,
	Thomas Abraham <thomas.ab@...sung.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 1/3] usb: udc: Fix gadget driver's speed check in various
 UDC drivers

On Sat, 19 Nov 2011, Michal Nazarewicz wrote:

> From: Michal Nazarewicz <mina86@...a86.com>
> 
> Several UDC drivers had a gadget driver's speed sanity check of the
> form of:
> 
> 	driver->speed != USB_SPEED_HIGH
> 
> or:
> 
> 	driver->speed != USB_SPEED_HIGH && driver->speed != USB_SPEED_FULL
> 
> As more and more gadget drivers support USB SuperSpeed, driver->speed
> may be set to USB_SPEED_SUPER and UDC driver should handle such gadget
> correctly.  The above checks however fail to recognise USB_SPEED_SUPER
> as a valid speed.
> 
> This commit changes the two checks to:
> 
> 	driver->speed < USB_SPEED_HIGH
> 
> or:
> 
> 	driver->speed < USB_SPEED_FULL
> 
> respectively.
> 
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> Reported-by: Alan Stern <stern@...land.harvard.edu>
> ---
> 
> I had no way of testing those changes but it appears that those UDC
> drivers check gadget driver's speed only on the entry point and then
> nothing is really dependent on it.

That's right; the idea is merely to avoid connecting at a speed that's
too fast for the gadget driver to handle.

> The only thing that makes me wonder a little is that
> USB_SPEED_WIRELESS will be allowed by the above checks and I'm not
> entirely sure if that's desired (even though that's probably not an
> issue right now).

I agree, wireless will eventually pose a problem.  Let's not worry 
about it for now, though.

> Nonetheless, this patch needs to get merged to 3.2 as without it
> file_storage won't work on UDC drivers this patch updates.
> 
> The next two patches that follow this one are replacements for
> [291a72f8: usb: gadget: replace usb_gadget::is_dualspeed with
> max_speed] and [d93bb846: usb: gadget: rename usb_gadget_driver::speed
> to max_speed] from Felipe's gadget tree, which did not apply correctly
> on top of this patch.

This all looks very good.  Thanks for doing the work.

Alan Stern

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