linux-kernel - Re: [PATCH] SDIO / PM: Add empty bus-level suspend/resume callbacks

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Message-ID: <20121202210106.GB22086@avionic-0098.adnet.avionic-design.de>
Date:	Sun, 2 Dec 2012 22:01:06 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	NeilBrown <neilb@...e.de>, Chris Ball <cjb@...top.org>,
	lkml <linux-kernel@...r.kernel.org>, linux-mmc@...r.kernel.org,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] SDIO / PM: Add empty bus-level suspend/resume callbacks

On Sun, Dec 02, 2012 at 02:48:50PM +0100, Rafael J. Wysocki wrote:
> On Sunday, December 02, 2012 07:46:25 PM NeilBrown wrote:
> > On Mon, 26 Mar 2012 00:29:24 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> > 
> > 
> > > Thanks for the confirmation.
> > > 
> > > Below it goes again with a changelog and tags.
> > > 
> > > I don't really think that SDIO does the right thing here overall, but that's
> > > all I can do to address the problem timely.
> > > 
> > > Thanks,
> > > Rafael
> > 
> > Hi Rafael,
> >  I just discovered that this patch has since been reverted - with an 'ack'
> >  from you:
> > ----------
> > commit d8e2ac330f65bcf47e8894fe5331a7e8ee019c06
> > Author: Thierry Reding <thierry.reding@...onic-design.de>
> > Date:   Thu Aug 9 09:32:21 2012 +0000
> > 
> >     mmc: sdio: Fix PM_SLEEP related build warnings
> >     
> >     Power management callbacks defined by SIMPLE_DEV_PM_OPS are only used if
> >     the PM_SLEEP Kconfig symbol has been defined. If not, the compiler will
> >     complain about them being unused. However, since the callback for this
> >     driver doesn't do anything it can just as well be dropped.
> >     
> >     Signed-off-by: Thierry Reding <thierry.reding@...onic-design.de>
> >     Acked-by: Rafael J. Wysocki <rjw@...k.pl>
> >     Signed-off-by: Chris Ball <cjb@...top.org>
> > -----------
> > 
> > Unsurprisingly the problem which your patch fixed has come back.
> > 
> > Do you think we could get the patch back in again.  This time maybe we should
> > put some comments in there pointing out that having a function which does
> > nothing is very different from not having any function at all?
> 
> Well, I agree.  I didn't remember that the callback had been added for
> a purpose and hence my "ack" for that patch.
> 
> What about applying the appended patch (hopefully, the build warnings should
> be fixed properly this time)?
> 
> Rafael
> 
> 
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Subject: SDIO / PM: Add empty bus-level suspend/resume callbacks
> 
> Suspend methods provided by SDIO drivers are not supposed to be
> called by the PM core.  Instead, when the SDIO core gets to suspend
> a device's ancestor, it calls the device driver's suspend routine.
> However, the PM core executes suspend callback routines directly for
> device drivers whose bus types don't provide suspend callbacks.
> In consequece, because the SDIO bus type doesn't provide a suspend
> callback, the SDIO drivers' suspend routines will be executed by the
> PM core (which shouldn't happen).
> 
> To prevent this from happening, add empty system suspend/resume
> callbacks for the SDIO bus type.
> 
> An analogous change had been made already by commit (e841a7c mmc:
> sdio: Use empty system suspend/resume callbacks at the bus level),
> but then it was reverted inadvertently by commit (d8e2ac3 mmc: sdio:
> Fix PM_SLEEP related build warnings) that attempted to fix build
> warnings introduced by commit e841a7c.
> 
> Reported-by: NeilBrown <neilb@...e.de>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/mmc/core/sdio_bus.c |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> Index: linux/drivers/mmc/core/sdio_bus.c
> ===================================================================
> --- linux.orig/drivers/mmc/core/sdio_bus.c
> +++ linux/drivers/mmc/core/sdio_bus.c
> @@ -193,7 +193,21 @@ static int sdio_bus_remove(struct device
>  }
>  
>  #ifdef CONFIG_PM
> +
> +#ifdef CONFIG_PM_SLEEP
> +static int pm_no_operation(struct device *dev)
> +{
> +	/*
> +	 * Prevent the PM core from calling SDIO device drivers' suspend
> +	 * callback routines, which it is not supposed to do, by using this
> +	 * empty function as the bus type suspend callaback for SDIO.
> +	 */
> +	return 0;
> +}
> +#endif
> +
>  static const struct dev_pm_ops sdio_bus_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(pm_no_operation, pm_no_operation)
>  	SET_RUNTIME_PM_OPS(
>  		pm_generic_runtime_suspend,
>  		pm_generic_runtime_resume,
> 

Hehe... if my memory serves me well, that's exactly (well, modulo the
comment) what my initial patch did before somebody suggested that the
empty callbacks should just be removed altogether. =)

Thierry

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