Re: [PATCH 11/41] rtc: ds1685: Convert to platform remove callback returning void

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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Hello Joshua,

On Mon, Mar 06, 2023 at 09:09:03PM -0500, Joshua Kinard wrote:
> On 3/6/2023 16:22, Uwe Kleine-König wrote:
> > On Mon, Mar 06, 2023 at 02:43:20PM -0500, Joshua Kinard wrote:
> > > On 3/4/2023 08:29, Uwe Kleine-König wrote:
> > > > The .remove() callback for a platform driver returns an int which makes
> > > > many driver authors wrongly assume it's possible to do error handling by
> > > > returning an error code. However the value returned is (mostly) ignored
> > > > and this typically results in resource leaks. To improve here there is a
> > > > quest to make the remove callback return void. In the first step of this
> > > > quest all drivers are converted to .remove_new() which already returns
> > > > void.
> > > > 
> > > > Trivially convert this driver from always returning zero in the remove
> > > > callback to the void returning variant.
> > > > 
> > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > > > ---
> > > >    drivers/rtc/rtc-ds1685.c | 6 ++----
> > > >    1 file changed, 2 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/rtc/rtc-ds1685.c b/drivers/rtc/rtc-ds1685.c
> > > > index 5db9c737c022..0f707be0eb87 100644
> > > > --- a/drivers/rtc/rtc-ds1685.c
> > > > +++ b/drivers/rtc/rtc-ds1685.c
> > > > @@ -1322,7 +1322,7 @@ ds1685_rtc_probe(struct platform_device *pdev)
> > > >     * ds1685_rtc_remove - removes rtc driver.
> > > >     * @pdev: pointer to platform_device structure.
> > > >     */
> > > > -static int
> > > > +static void
> > > >    ds1685_rtc_remove(struct platform_device *pdev)
> > > >    {
> > > >    	struct ds1685_priv *rtc = platform_get_drvdata(pdev);
> > > > @@ -1344,8 +1344,6 @@ ds1685_rtc_remove(struct platform_device *pdev)
> > > >    	rtc->write(rtc, RTC_EXT_CTRL_4A,
> > > >    		   (rtc->read(rtc, RTC_EXT_CTRL_4A) &
> > > >    		    ~(RTC_CTRL_4A_RWK_MASK)));
> > > > -
> > > > -	return 0;
> > > >    }
> > > >    /*
> > > > @@ -1356,7 +1354,7 @@ static struct platform_driver ds1685_rtc_driver = {
> > > >    		.name	= "rtc-ds1685",
> > > >    	},
> > > >    	.probe		= ds1685_rtc_probe,
> > > > -	.remove		= ds1685_rtc_remove,
> > > > +	.remove_new	= ds1685_rtc_remove,
> > > >    };
> > > >    module_platform_driver(ds1685_rtc_driver);
> > > >    /* ----------------------------------------------------------------------- */
> > > 
> > > Is there a future planned patch that would remove the .remove member
> > > and then rename .remove_new --> .remove?
> > 
> > The eventual plan is to do
> > 
> > diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> > diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> > index 77510e4f47de..1c65943d6b53 100644
> > --- a/drivers/base/platform.c
> > +++ b/drivers/base/platform.c
> > @@ -1420,14 +1420,8 @@ static void platform_remove(struct device *_dev)
> >   	struct platform_driver *drv = to_platform_driver(_dev->driver);
> >   	struct platform_device *dev = to_platform_device(_dev);
> > -	if (drv->remove_new) {
> > -		drv->remove_new(dev);
> > -	} else if (drv->remove) {
> > -		int ret = drv->remove(dev);
> > -
> > -		if (ret)
> > -			dev_warn(_dev, "remove callback returned a non-zero value. This will be ignored.\n");
> > -	}
> > +	if (drv->remove)
> > +		drv->remove(dev);
> >   	dev_pm_domain_detach(_dev, true);
> >   }
> > index b845fd83f429..8c5fdaa8645f 100644
> > --- a/include/linux/platform_device.h
> > +++ b/include/linux/platform_device.h
> > @@ -209,15 +209,16 @@ struct platform_driver {
> >   	int (*probe)(struct platform_device *);
> >   	/*
> > -	 * Traditionally the remove callback returned an int which however is
> > +	 * Traditionally the remove callback returned an int which however was
> >   	 * ignored by the driver core. This led to wrong expectations by driver
> >   	 * authors who thought returning an error code was a valid error
> > -	 * handling strategy. To convert to a callback returning void, new
> > -	 * drivers should implement .remove_new() until the conversion it done
> > -	 * that eventually makes .remove() return void.
> > +	 * handling strategy. .remove_new is a hangover from these times which
> > +	 * will be dropped once all drivers are converted to .remove().
> >   	 */
> > -	int (*remove)(struct platform_device *);
> > -	void (*remove_new)(struct platform_device *);
> > +	union {
> > +		void (*remove)(struct platform_device *);
> > +		void (*remove_new)(struct platform_device *);
> > +	};
> >   	void (*shutdown)(struct platform_device *);
> >   	int (*suspend)(struct platform_device *, pm_message_t state);
> > 
> > and then once all the drivers are converted back to .remove() drop the
> > union and .remove_new().
> > 
> > Best regards
> > Uwe
> > 
> 
> This looks like a pretty simple/minor API change.  Why not just do a patch
> series that makes both the API change and updates all of the drivers at once
> (one commit per driver)?

A bit of statistic: Based on v6.3-rc1 I have 2286 patches like the ones
from this series that (mostly) convert drivers that today already return
zero unconditionally. Then there is my todo-list of ~100 additional
drivers that don't return 0 that need manual inspection and fixing.

So we're talking about 2300+ drivers in all subsystems here. To get a
bisectable series that does the complete conversion, we need:

	2300 patches to convert drivers to .remove_new()
	the above patch
	2300 patches to convert drivers back to the new .remove()

Last time I sent a series with ~640 patches (for a similar conversion
for i2c drivers) people were unlucky already and I got tons of bounces.
Please consider the address list for the cover letter. While most
patches are trivial this would require a massive coordination.

So no, this isn't a sensible suggestion. I'll continue to send out
conversions to .remove_new() per subsystem and once most of them are
converted, the above patch will be sent with the remainder of the
unapplied patches.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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