linux-kernel - Re: [PATCH 04/26] usb: gadget: introduce 'enabled' flag in struct usb

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Date:	Tue, 15 Sep 2015 18:15:25 +0200
From:	Krzysztof Opasiak <k.opasiak@...sung.com>
To:	balbi@...com
Cc:	Robert Baldyga <r.baldyga@...sung.com>, gregkh@...uxfoundation.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	b.zolnierkie@...sung.com, m.szyprowski@...sung.com,
	andrzej.p@...sung.com
Subject: Re: [PATCH 04/26] usb: gadget: introduce 'enabled' flag in struct
 usb_ep



On 09/15/2015 05:43 PM, Felipe Balbi wrote:
> On Tue, Sep 15, 2015 at 05:37:27PM +0200, Krzysztof Opasiak wrote:
>> Hello,
>>
>> On 09/15/2015 04:26 PM, Robert Baldyga wrote:
>>> This patch introduces 'enabled' flag in struct usb_ep, and modifies
>>> usb_ep_enable() and usb_ep_disable() functions to encapsulate endpoint
>>> enabled/disabled state. It helps to avoid enabling endpoints which are
>>> already enabled, and disabling endpoints which are already disables.
>>>
>>> >From now USB functions don't have to remember current endpoint
>>> enable/disable state, as this state is now handled automatically which
>>> makes this API less bug-prone.
>>>
>>> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
>>> ---
>>>   include/linux/usb/gadget.h | 21 +++++++++++++++++++--
>>>   1 file changed, 19 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
>>> index 3f299e2..63375cd 100644
>>> --- a/include/linux/usb/gadget.h
>>> +++ b/include/linux/usb/gadget.h
>>> @@ -215,6 +215,7 @@ struct usb_ep {
>>>   	struct list_head	ep_list;
>>>   	struct usb_ep_caps	caps;
>>>   	bool			claimed;
>>> +	bool			enabled;
>>>   	unsigned		maxpacket:16;
>>>   	unsigned		maxpacket_limit:16;
>>>   	unsigned		max_streams:16;
>>> @@ -264,7 +265,15 @@ static inline void usb_ep_set_maxpacket_limit(struct usb_ep *ep,
>>>    */
>>>   static inline int usb_ep_enable(struct usb_ep *ep)
>>>   {
>>> -	return ep->ops->enable(ep, ep->desc);
>>> +	int ret = 0;
>>> +
>>> +	if (!ep->enabled) {
>>> +		ret = ep->ops->enable(ep, ep->desc);
>>> +		if (!ret)
>>> +			ep->enabled = true;
>>> +	}
>>> +
>>> +	return ret;
>>>   }
>>>
>>>   /**
>>> @@ -281,7 +290,15 @@ static inline int usb_ep_enable(struct usb_ep *ep)
>>>    */
>>>   static inline int usb_ep_disable(struct usb_ep *ep)
>>>   {
>>> -	return ep->ops->disable(ep);
>>> +	int ret = 0;
>>> +
>>> +	if (ep->enabled) {
>>> +		ret = ep->ops->disable(ep);
>>> +		if (!ret)
>>> +			ep->enabled = false;
>>> +	}
>>> +
>>> +	return ret;
>>>   }
>>>
>>
>> Personally I don't like this convention. In my opinion usb_ep_disable() &
>> usb_ep_enable() should fail if ep is already disabled/enabled. Then in
>> function code we should check if endpoint is enabled (maybe even we should
>> have usb_ep_is_enabled()) and call disable only when it is really enabled.
>
> usb_ep_is_enabled() should be a good addition but I don't see an issue
> ignoring usb_ep_enabled() for something that's already enabled.
>
> Imagine if you got an error when you tried to push the light switch to
> the 'on' position while the light was already on :-p
>

Hmmm not sure right now, didn't test this recently :D as usually I check 
if light isn't already "on" before I touch the switch to turn it on:P

Just joking. Personally I just prefer to don't touch things which are 
already in desired condition. Let's take close() as example which could 
be a little bit equivalent of our usb_ep_disable(). It is not legal to 
call it twice on some fd and second call ends up with error.

Best regards,

-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
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