linux-kernel - Re: [PATCH v5 01/46] usb: gadget: encapsulate endpoint claiming mechanism

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Date:	Thu, 20 Aug 2015 20:07:35 +0000
From:	John Youn <John.Youn@...opsys.com>
To:	"balbi@...com" <balbi@...com>,
	Robert Baldyga <r.baldyga@...kerion.com>
CC:	Robert Baldyga <r.baldyga@...sung.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"Peter.Chen@...escale.com" <Peter.Chen@...escale.com>,
	"John.Youn@...opsys.com" <John.Youn@...opsys.com>,
	"dahlmann.thomas@...or.de" <dahlmann.thomas@...or.de>,
	"nicolas.ferre@...el.com" <nicolas.ferre@...el.com>,
	"cernekee@...il.com" <cernekee@...il.com>,
	"leoli@...escale.com" <leoli@...escale.com>,
	"daniel@...que.org" <daniel@...que.org>,
	"haojian.zhuang@...il.com" <haojian.zhuang@...il.com>,
	"robert.jarzmik@...e.fr" <robert.jarzmik@...e.fr>,
	"michal.simek@...inx.com" <michal.simek@...inx.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-geode@...ts.infradead.org" <linux-geode@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"andrzej.p@...sung.com" <andrzej.p@...sung.com>,
	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"petr.cvek@....cz" <petr.cvek@....cz>
Subject: Re: [PATCH v5 01/46] usb: gadget: encapsulate endpoint claiming
 mechanism

On 8/20/2015 10:45 AM, Felipe Balbi wrote:
> Hi,
> 
> On Thu, Aug 20, 2015 at 07:16:48PM +0200, Robert Baldyga wrote:
>> On 08/20/2015 06:48 PM, Felipe Balbi wrote:
>>> On Thu, Aug 20, 2015 at 06:28:14PM +0200, Robert Baldyga wrote:
>>>> Hi Felipe,
>>>>
>>>> On 08/20/2015 05:35 PM, Felipe Balbi wrote:
>>>> [...]
>>>>> just letting you know that this regresses all gadget drivers making them
>>>>> try to disable previously disabled endpoints and enable previously
>>>>> enabled endpoints.
>>>>>
>>>>> I have a possible fix (see below) but then it shows a problem on the
>>>>> host side when using with g_zero (see further below):
>>>>>
>>>>> commit 3b8932100aacb6cfbffe288ca93025d8b8430c00
>>>>> Author: Felipe Balbi <balbi@...com>
>>>>> Date:   Wed Aug 19 18:05:27 2015 -0500
>>>>>
>>>>>     usb: gadget: fix ep->claimed lifetime
>>>>>
>>>>>     In order to fix a regression introduced by commit
>>>>>     cc476b42a39d ("usb: gadget: encapsulate endpoint
>>>>>     claiming mechanism") we have to introduce a simple
>>>>>     helper to check if a particular is enabled or not.
>>>>>
>>>>>     After that, we need to move ep->claimed lifetime to
>>>>>     usb_ep_enable() and usb_ep_disable() since those
>>>>>     are the only functions which actually enable and
>>>>>     disable endpoints.
>>>>>
>>>>>     A follow-up patch will come to drop all driver_data
>>>>>     checks from function drivers, since those are, now,
>>>>>     pointless.
>>>>>
>>>>>     Fixes: cc476b42a39d ("usb: gadget: encapsulate endpoint
>>>>>     	claiming mechanism")
>>>>>     Cc: Robert Baldyga <r.baldyga@...sung.com>
>>>>>     Signed-off-by: Felipe Balbi <balbi@...com>
>>>>>
>>>>> diff --git a/drivers/usb/gadget/epautoconf.c b/drivers/usb/gadget/epautoconf.c
>>>>> index 978435a51038..ad45070cd76f 100644
>>>>> --- a/drivers/usb/gadget/epautoconf.c
>>>>> +++ b/drivers/usb/gadget/epautoconf.c
>>>>> @@ -126,7 +126,6 @@ found_ep:
>>>>>  	ep->address = desc->bEndpointAddress;
>>>>>  	ep->desc = NULL;
>>>>>  	ep->comp_desc = NULL;
>>>>> -	ep->claimed = true;
>>>>
>>>> Removing this line causes autoconfig can return the same endpoint many
>>>> times. This probably causes problems with g_zero.
>>>>
>>>> I will try to fix it ASAP.
>>>
>>> I was considering the same thing, but the lifetime of ->claimed doesn't
>>> look correct to me either way. Note that once the flag is enabled, it
>>> won't get disabled by most gadget drivers.
>>
>> And it should not be. This flag is indicator, that endpoint is used by some
>> function. It should be set once by usb_ep_autoconfig() and cleared by
>> usb_ep_autoconfig_reset().

And the 'claimed' flag should be used for the ep autoconfig
mechanism alone. We may want to reset it during the autoconfig
phase for multiple configs and alt-interfaces. So there should be
separate 'claimed' and 'enabled' flags.


> 
> have you considered switching interfaces and/or alternate settings ?

We ran into similar issues before with this very scenario. Handling
of set_config(0 or N), in both addressed and configured states, and
set_interface requests.


John

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