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 10:10:28 -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 05:14:42PM +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?

thanks,

greg k-h
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