linux-kernel - Re: [PATCH 10/10] drivers: misc: use module_platform_driver

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Date:	Wed, 20 Mar 2013 11:46:07 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Fabio Porcedda <fabio.porcedda@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	H Hartley Sweeten <hartleys@...ionengravers.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH 10/10] drivers: misc: use module_platform_driver_probe()

On Wednesday 20 March 2013, Fabio Porcedda wrote:
> 
> On Wed, Mar 20, 2013 at 11:20 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Wednesday 20 March 2013, Fabio Porcedda wrote:
> >> I think we can check inside the  deferred_probe_work_func()
> >> if the dev->probe function pointer is equal to platform_drv_probe_fail().
> >
> > I think it's too late by then, because that would only warn if we try to probe
> > it again, but when platform_driver_probe() does not succeed immediately, it
> 
> Maybe you mean "does succeed immediately" ?

I mean in this code (simplified for the sake of discussion)

int __init_or_module platform_driver_probe(struct platform_driver *drv,
                int (*probe)(struct platform_device *))
{
        int retval, code;

        drv->probe = probe;
        retval = code = platform_driver_register(drv);

        drv->probe = NULL;
        if (code == 0 && list_empty(&drv->driver.p->klist_devices.k_list))
                retval = -ENODEV;
        drv->driver.probe = platform_drv_probe_fail;

        if (code != retval)
                platform_driver_unregister(drv);
        return retval;
}

we assume that all devices are bound to drivers during the call to
platform_driver_register, and if the device list is empty afterwards,
we unregister the driver and will never get to the deferred probing
stage.

	Arnd
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