linux-kernel - Re: [PATCH 3/5] usb: xhci: Correct last context entry calculation for Configure Endpoint

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Date:	Tue, 24 Jun 2014 10:47:37 -0400
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	dan.j.williams@...el.com, Julius Werner <jwerner@...omium.org>
Subject: Re: [PATCH 3/5] usb: xhci: Correct last context entry calculation
 for Configure Endpoint

On Tue, Jun 24, 2014 at 05:51:16PM +0300, Mathias Nyman wrote:
> On 06/24/2014 05:10 PM, Greg KH wrote:
> > On Tue, Jun 24, 2014 at 05:14:42PM +0300, Mathias Nyman wrote:
> >> From: Julius Werner <jwerner@...omium.org>
> >>
> >> The current XHCI driver recalculates the Context Entries field in the
> >> Slot Context on every add_endpoint() and drop_endpoint() call. In the
> >> case of drop_endpoint(), it seems to assume that the add_flags will
> >> always contain every endpoint for the new configuration, which is not
> >> necessarily correct if you don't make assumptions about how the USB core
> >> uses the add_endpoint/drop_endpoint interface (add_flags only contains
> >> endpoints that are new additions in the new configuration).
> >>
> >> Furthermore, EP0_FLAG is not consistently set in add_flags throughout
> >> the lifetime of a device. This means that when all endpoints are
> >> dropped, the Context Entries field can be set to 0 (which is invalid and
> >> may cause a Parameter Error) or -1 (which is interpreted as 31 and
> >> causes the driver to keep using the old, incorrect value).
> >>
> >> The only surefire way to set this field right is to also take all
> >> existing endpoints into account, and to force the value to 1 (meaning
> >> only EP0 is active) if no other endpoint is found. This patch implements
> >> that as a single step in the final check_bandwidth() call and removes
> >> the intermediary calculations from add_endpoint() and drop_endpoint().
> >>
> >> Signed-off-by: Julius Werner <jwerner@...omium.org>
> >> Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
> >> ---
> >>  drivers/usb/host/xhci.c | 51 +++++++++++++++++--------------------------------
> >>  1 file changed, 18 insertions(+), 33 deletions(-)
> > 
> > Is this something for older (i.e. stable) kernels?
> > 
> 
> This was intentionally left out of stable, reasoning in a previous mail was:
> 
> "We discussed with Sarah that we should try this out and queue it for 
> usb-linus. This clearly fixes the generation of a invalid slot context 
> if all endpoints are dropped.
> 
> But because there hasn't been any reported issue about the other case 
> this changes (always setting context entries to last valid ep in target 
> configuration), and spec still has this tiny contradiction in this case, 
> we should keep this out of stable. At least for now, until it gets some 
> real world testing coverage."
> 
> The mail:
> http://marc.info/?l=linux-usb&m=139879120000807&w=2
> 
> Or if you prefer this patch could go to usb-next instead.

If it doesn't fix a known issue, then it shouldn't go to 3.16-final at
this point in time, as I can't justify it being added.  So I'll queue it
up for usb-next instead right now.

thanks,

greg k-h
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