linux-kernel - Re: [PATCH 2/3] PWM: vt8500: Update vt8500 PWM driver support

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Message-Id: <201210221352.08352.arnd@arndb.de>
Date:	Mon, 22 Oct 2012 13:52:08 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	Tony Prisk <linux@...sktech.co.nz>, arm@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH 2/3] PWM: vt8500: Update vt8500 PWM driver support

On Monday 22 October 2012, Thierry Reding wrote:
> > As long as we get build warnings for leaving out the __devinit/__devexit
> > annotations, I would generally recommend putting them in. If we do a
> > patch to remove all of them, a couple extra instances will not cause
> > any more troubles than we already have.
> 
> I've never seen any build warnings for leaving __devinit/__devexit out.
> Where does that happen?

Section mismatches usually result into warnings from modpost, like

WARNING: modpost: Found 1 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

Actually doing that gives you an output like this (currently on exynos_defconfig):

$ make CONFIG_DEBUG_SECTION_MISMATCH=y
WARNING: drivers/pinctrl/built-in.o(.devinit.text+0x124): Section mismatch in reference from the function samsung_pinctrl_probe() to the function .init.text:samsung_gpiolib_register()
The function __devinit samsung_pinctrl_probe() references
a function __init samsung_gpiolib_register().
If samsung_gpiolib_register is only used by samsung_pinctrl_probe then
annotate samsung_gpiolib_register with a matching annotation.

or like this (now fixed in socfpga_defconfig):

WARNING: drivers/net/ethernet/stmicro/stmmac/stmmac.o(.text+0x5d4c): Section mismatch in reference from the function stmmac_pltfr_probe() to the function .devinit.text:stmmac_probe_config_dt()
The function stmmac_pltfr_probe() references
the function __devinit stmmac_probe_config_dt().
This is often because stmmac_pltfr_probe lacks a __devinit 
annotation or the annotation of stmmac_probe_config_dt is wrong.

I believe you normally don't get warnings for functions that could be
marked __devinit and only call regular functions, but there are
a couple of __devinit infrastructure functions that you can't call
from a function that isn't __init or __devinit.

	Arnd
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