linux-kernel - Re: [PATCH] driver core: Move deferred devices to the end of dpm

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Message-Id: <201207051515.34019.rjw@sisk.pl>
Date:	Thu, 5 Jul 2012 15:15:33 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: Move deferred devices to the end of dpm_list before probing

On Thursday, July 05, 2012, Mark Brown wrote:
> When deferred probe was originally added the idea was that devices which
> defer their probes would move themselves to the end of dpm_list in order
> to try to keep the assumptions that we're making about the list being in
> roughly the order things should be suspended correct. However this hasn't
> been what's been happening and doing it requires a lot of duplicated code
> to do the moves.
> 
> Instead take a simple, brute force solution and have the deferred probe
> code push devices to the end of dpm_list before it retries the probe. This
> does mean we lock the dpm_list a bit more often but it's very simple and
> the code shouldn't be a fast path. We do the move with the deferred mutex
> dropped since doing things with fewer locks held simultaneously seems like
> a good idea.
> 
> This approach was most recently suggested by Grant Likely.
> 
> Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>

Looks good.

Acked-by: Rafael J. Wysocki <rjw@...k.pl>

> ---
>  drivers/base/dd.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 6cd2c6c..9b0aca4 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -85,8 +85,20 @@ static void deferred_probe_work_func(struct work_struct *work)
>  		 * manipulate the deferred list
>  		 */
>  		mutex_unlock(&deferred_probe_mutex);
> +
> +		/*
> +		 * Force the device to the end of the dpm_list since
> +		 * the PM code assumes that the order we add things to
> +		 * the list is a good order for suspend but deferred
> +		 * probe makes that very unsafe.
> +		 */
> +		device_pm_lock();
> +		device_pm_move_last(dev);
> +		device_pm_unlock();
> +
>  		dev_dbg(dev, "Retrying from deferred list\n");
>  		bus_probe_device(dev);
> +
>  		mutex_lock(&deferred_probe_mutex);
>  
>  		put_device(dev);
> 

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