linux-kernel - Re: [PATCH] usb: echi-hcd: Add register access check in shutdown

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Date:	Wed, 18 May 2016 14:54:25 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<andy.gross@...aro.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: echi-hcd: Add register access check in shutdown

On Wed, 18 May 2016, Srinivas Kandagatla wrote:

> On 18/05/16 15:56, Alan Stern wrote:
> > This doesn't seem like the right place.  What you really should do is
> > skip calling ehci_silence_controller() if the hardware isn't
> > accessible.  That's where the hardware gets touched, not in
> > ehci_shutdown().
> 
> Just tried this suggestion, this would not work as well, Its not just 
> the hardware registers, which are of concern here, but also the rest of 
> the things like ehci->hrtimer pointer which are allocated or initialized 
> as part of ehci_setup().
> 
> Either the msm controller driver is not correct or we should have a way 
> to stop calling ehci_shutdown() if there was no ehci_setup() done yet.
> 
> Any suggestions?

Yes, you're right.

Since you're concerned about more than just accessing the hardware 
registers, HW_ACCESSIBLE isn't the right thing to test.  You need 
something that gets set in ehci_setup() and nowhere else.

One possibility is ehci->sbrn.  If that is equal to 0 then ehci_setup() 
hasn't run, so ehci->shutdown() can simply return.  Be sure to put a 
comment in the code explaining the reason for doing this.

Alan Stern