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

Felipe Balbi
2015-09-15T15:43:32Z

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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@samsung.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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