linux-kernel - RE: [PATCH 3/8][v2]usb:fsl:otg: Add support to add/remove usb host driver

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Date:	Mon, 10 Aug 2015 10:44:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ramneek Mehresh <ramneek.mehresh@...escale.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Li Leo <LeoLi@...escale.com>
Subject: RE: [PATCH 3/8][v2]usb:fsl:otg: Add support to add/remove usb host
 driver

On Mon, 10 Aug 2015, Ramneek Mehresh wrote:

> > Also, what is the reason for calling usb_hcd_resume_root_hub()?  It won't
> > do anything, because it will run before the scheduled work, so there won't
> > be a root hub for it to resume.
> > 
> Well, you're right...it's not a surety that usb_hcd_resume_root_hub() will run after
> scheduled work...i'll move it inside do_change_hcd() after usb_add_hcd(). Thanks.

You're missing the point.  There's no reason ever to call 
usb_hcd_resume_root_hub() immediately after usb_add_hcd().  The hub 
driver does everything necessary when the root hub is registered.  
Resuming it (if it is suspended at that point) won't accomplish 
anything because all the important work has just been done.

Now, if you _weren't_ calling usb_add_hcd() (for example if host.is_otg
were 0) then it might make sense to call usb_hcd_resume_root_hub() --
although I don't see why you would need to.

Alan Stern

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