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

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Message-ID: <5335A824.2060204@linux.intel.com>
Date:	Fri, 28 Mar 2014 18:49:40 +0200
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	Julius Werner <jwerner@...omium.org>,
	Mathias Nyman <mathias.nyman@...el.com>
CC:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Vincent Palatin <vpalatin@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Jim Lin <jilin@...dia.com>
Subject: Re: [PATCH] usb: xhci: Correct last context entry calculation for
 Configure Endpoint

On 03/25/2014 08:42 PM, Julius Werner wrote:
> 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().
>

Hi

I think this looks good in general, but before I really dig into it I'd 
like to know if this has triggered any problems so far? (e.g. slot 
context's context entries getting zeroed, or set to a smaller value than 
the last active endpoint context,  causing trouble)

-Mathias



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