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

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Date:	Tue, 15 Sep 2015 10:43:24 -0500
From:	Felipe Balbi <balbi@...com>
To:	Krzysztof Opasiak <k.opasiak@...sung.com>
CC:	Robert Baldyga <r.baldyga@...sung.com>, <balbi@...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 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()

-- 
balbi

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