linux-kernel - Re: [PATCH] PM / USB: hcd_pci: Skip secondary root hub check for HCD

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Date:   Tue, 25 Jul 2017 10:05:03 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
cc:     Linux USB <linux-usb@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Felipe Balbi <balbi@...nel.org>
Subject: Re: [PATCH] PM / USB: hcd_pci: Skip secondary root hub check for
 HCD_DEAD()

On Tue, 25 Jul 2017, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If HCD_DEAD(hcd) is "true" in check_root_hub_suspended(), it is
> rather pointless to check the secondary root hub, so return early
> then.
> 
> This actually fixes occasional suspend failures on one of my test
> machines.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/usb/core/hcd-pci.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-pm/drivers/usb/core/hcd-pci.c
> ===================================================================
> --- linux-pm.orig/drivers/usb/core/hcd-pci.c
> +++ linux-pm/drivers/usb/core/hcd-pci.c
> @@ -427,6 +427,9 @@ static int check_root_hub_suspended(stru
>  		dev_warn(dev, "Root hub is not suspended\n");
>  		return -EBUSY;
>  	}
> +	if (HCD_DEAD(hcd))
> +		return 0;
> +
>  	if (hcd->shared_hcd) {
>  		hcd = hcd->shared_hcd;
>  		if (HCD_RH_RUNNING(hcd)) {

While this is an okay solution, IMO it would be more reliable and more 
general to have usb_hc_died() clear the HCD_FLAG_RH_RUNNING bit and set 
the HCD_FLAG_DEAD bit in the shared hcd.  Right now it only does these 
things for the primary.

Would you like to write and test a patch to do that?

Incidentally, if this fixes occasional suspend failures on your test 
machine, does that mean the test machine's host controller occasionally 
dies?  Maybe that should be fixed too...

Alan Stern