linux-kernel - Re: [PATCH] USB: output an error message when the pipe type doesn't match the endpoint type

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Date:	Wed, 1 Sep 2010 13:49:17 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Simon Arlott <simon@...e.lp0.eu>
cc:	Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] USB: output an error message when the pipe type doesn't
 match the endpoint type

On Wed, 1 Sep 2010, Simon Arlott wrote:

> > This is okay with me.  If you're serious about not changing the
> > behavior merely because debugging is enabled, you could move this test
> > out of the debug-only region and possibly change the dev_err to
> > dev_dbg.  However doing so might break some devices that are currently
> > working.
> 
> I'd expect that to break potentially many devices, although only cxacru
> stopped working for me. The USB API isn't really suitable for adding
> this type of check because it allows the drivers to get away with too
> much already.

Unlike device hardware, drivers can always be changed.  If adding a 
check will help spot errors, it's probably worthwhile.

> usb_clear_halt() takes a pipe when it really wants the endpoint, the
> pipe type is ignored.

What's wrong with that?  Besides, in the end we shouldn't be using
pipes at all; we should always use pointers to struct
usb_host_endpoint.

> usb_bulk_msg() auto-detects the type between interrupt and bulk, as
> does usb_interrupt_msg() because the latter just calls the former.
> 
> (I think -EINVAL might be a better return code. The pipe isn't broken,
> it doesn't exist.)

Within the kernel, the meanings of the -Exxx error codes are fairly
arbitrary.  But since this code can be passed to userspace you are
right.

Alan Stern

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