linux-kernel - Re: [RFC 1/1] driver core: re-order dpm

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Date:	Fri, 12 Dec 2014 10:34:02 -0500
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Grant Likely <grant.likely@...aro.org>,
	Bill Huang <bilhuang@...dia.com>
Cc:	vinceh@...dia.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] driver core: re-order dpm_list after a succussful probe

On Fri, Dec 12, 2014 at 03:50:15AM -0800, Bill Huang wrote:
> The dpm_list was added in the call "device_add" and when we do defer
> probe we'll explicitly move the probed device to be the last in the
> dpm_list, we should do the same for the normal probe since there are
> cases that we won't have chance to do defer probe to change the PM order
> as the below example.
> 
> If we would like the device driver A to be suspended earlier than the
> device driver B, we won't have chance to do defer probe to fix the
> suspend dependency since at the time device driver A is probed, device B
> was up and running.
> 
> Device A was added
> Device B was added
> Driver for device B was binded
> Driver for device A was binded
> 
> Signed-off-by: Bill Huang <bilhuang@...dia.com>
> ---
> 
> It seems to me this is a bug in the core driver, but I'm not sure how should
> we fix it.
> 
> - Do we have better fix?
> - This proposed fix or any other fix might introduces side effect that breaks
>   existing working suspend dependencies which happen to work based on the
>   existing wrong suspend order.
> 
> Any thoughts? Thanks.
> 
>  drivers/base/dd.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index cdc779c..54886d2 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -308,6 +308,10 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>  			goto probe_failed;
>  	}
>  
> +	device_pm_lock();
> +	device_pm_move_last(dev);
> +	device_pm_unlock();
> +
>  	driver_bound(dev);
>  	ret = 1;
>  	pr_debug("bus: '%s': %s: bound device %s to driver %s\n",


Adding Grant, as he did the deferred probe stuff...

And it's the middle of the merge window, I'll not have time to look at
this for a few weeks at the earliest, sorry.

thanks,

greg k-h
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