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

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Date:	Tue, 19 Mar 2013 10:04:32 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Fabio Porcedda <fabio.porcedda@...il.com>,
	Arnd Bergmann <arnd@...db.de>
Cc:	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>,
	Hans-Christian Egtvedt <hans-christian.egtvedt@...el.com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH 10/10] drivers: misc: use module_platform_driver_probe()

On Tue, Mar 19, 2013 at 9:55 AM, Fabio Porcedda
<fabio.porcedda@...il.com> wrote:
> On Mon, Mar 18, 2013 at 12:28 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Monday 18 March 2013, Fabio Porcedda wrote:
>>> On Mon, Mar 18, 2013 at 11:58 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>> > On Monday 18 March 2013, Fabio Porcedda wrote:
>>> >> Since by using platform_driver_probe() the  function
>>> >> ep93xx_pwm_probe() is freed after initialization,
>>> >> is better to use module_platform_drive_probe().
>>> >> IMHO i don't see any good reason to use module_platform_driver() for
>>> >> this driver.
>>> >
>>> > As I commented earlier, the platform_driver_probe() and
>>> > module_platform_drive_probe() interfaces are rather dangerous in combination
>>> > with deferred probing, I would much prefer Harley's patch.
>>>
>>> Since those drivers don't use -EPROBE_DEFER i was thinking that they don't use
>>> deferred probing.
>>> I'm missing something?
>>
>> clk_get() may return -EPROBE_DEFER after ep93xx is converted to use the
>> common clk API. We currently return the value of clk_get from the probe()
>> function, which will automatically do the right thing as long as the probe
>> function remains reachable.
>
> Thanks for the explanation.

Hmm, so we may have drivers that (now) work perfectly fine with
module_platform_driver_probe()/platform_driver_probe(), but will start
failing suddenly in the future?

I guess we need a big fat WARN_ON(-EPROBE_DEFER) in
platform_driver_probe() to catch these?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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