linux-kernel - Re: [PATCH 3/7] PCI PM: Fix saving of device state in pci_legacy

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Date:	Wed, 04 Feb 2009 12:56:53 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 3/7] PCI PM: Fix saving of device state in
 pci_legacy_suspend

On Wed, 2009-02-04 at 01:59 +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> Make pci_legacy_suspend() save the state of the device if it is
> in PCI_UNKNOWN after its suspend callback has run and warn only if
> the power state of the device has been changed by its suspend
> callback.
> 
> Also, use WARN_ONCE(), which is more useful, in pci_legacy_suspend(),
> so that the name of the offending function is printed.
> 
> Additionaly, remove the unnecessary line of code setting
> pci_dev->state_saved.

Minor nit: Should the warning be preceeded by a message ? The reason is,
right now, all we get is a backtrace, it doesn't actually tell you which
device or driver caused it which makes it pretty pointless.

I think you should add a printk(KERN_ERR... just before that which gives
those informations along with a little blurb along the lines of "driver
changed device state without saving config space state").

> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> Reported-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
>  drivers/pci/pci-driver.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/drivers/pci/pci-driver.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci-driver.c
> +++ linux-2.6/drivers/pci/pci-driver.c
> @@ -355,6 +355,8 @@ static int pci_legacy_suspend(struct dev
>  	int i = 0;
>  
>  	if (drv && drv->suspend) {
> +		pci_power_t prev = pci_dev->current_state;
> +
>  		pci_dev->state_saved = false;
>  
>  		i = drv->suspend(pci_dev, state);
> @@ -365,12 +367,16 @@ static int pci_legacy_suspend(struct dev
>  		if (pci_dev->state_saved)
>  			goto Fixup;
>  
> -		if (WARN_ON_ONCE(pci_dev->current_state != PCI_D0))
> +		if (pci_dev->current_state != PCI_D0
> +		    && pci_dev->current_state != PCI_UNKNOWN) {
> +			WARN_ONCE(pci_dev->current_state != prev,
> +				"PCI PM: Device state not saved by %pF\n",
> +				drv->suspend);
>  			goto Fixup;
> +		}
>  	}
>  
>  	pci_save_state(pci_dev);
> -	pci_dev->state_saved = true;
>  	/*
>  	 * This is for compatibility with existing code with legacy PM support.
>  	 */

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