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

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Date:	Tue, 15 Sep 2015 11:01:31 -0500
From:	Felipe Balbi <balbi@...com>
To:	Robert Baldyga <r.baldyga@...sung.com>
CC:	<balbi@...com>, Krzysztof Opasiak <k.opasiak@...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

Hi,

On Tue, Sep 15, 2015 at 05:57:53PM +0200, Robert Baldyga wrote:
> 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
> > 
> > I do think, though, that this can be simplified by returning early if
> > already enabled:
> > 
> > usb_ep_enable()
> > {
> > 	if (ep->enabled)
> > 		return 0;
> > 
> > 	return ep->ops->enable(ep, ep->desc);
> > }
> > 
> > and likewise for usb_ep_disable()
> 
> We can't do that, because we need to toggle ep->enable flag.

man, things have to be spelled out to the last comma... The point was to
avoid the extra identation level

usb_ep_enable()
{
	int ret;

	if (ep->enabled)
		return 0;

	ret = ep->ops->enable(ep, ep->desc);
	if (ret)
		return ret;

	ep->enabled = true;

	return 0;
}

-- 
balbi

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