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Date: Thu, 17 Jul 2014 12:48:57 +0200 From: Arnd Bergmann <arnd@...db.de> To: Lars-Peter Clausen <lars@...afoo.de> Cc: Chen Gang <gang.chen.5i5j@...il.com>, Guenter Roeck <linux@...ck-us.net>, Richard Weinberger <richard@....at>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, dmitry.torokhov@...il.com, linux-iio@...r.kernel.org, Benjamin Herrenschmidt <benh@...nel.crashing.org>, teg@...m.no, Thierry Reding <thierry.reding@...il.com>, Lennox Wu <lennox.wu@...il.com>, Marek Vasut <marex@...x.de>, Liqin Chen <liqin.linux@...il.com>, msalter@...hat.com, linux-pwm@...r.kernel.org, devel@...verdev.osuosl.org, linux-watchdog@...r.kernel.org, linux-input@...r.kernel.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, knaack.h@....de, Martin Schwidefsky <schwidefsky@...ibm.com>, Mischa.Jonker@...opsys.com, jic23@...nel.org, Geert Uytterhoeven <geert@...ux-m68k.org> Subject: Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for 'devm_ioremap_resource' On Thursday 17 July 2014 12:40:25 Lars-Peter Clausen wrote: > On 07/17/2014 11:20 AM, Arnd Bergmann wrote: > > On Thursday 17 July 2014 09:27:58 Chen Gang wrote: > >> gfp_t gfp_mask, unsigned int order); > >> extern void devm_free_pages(struct device *dev, unsigned long addr); > >> > >> +#ifdef CONFIG_HAS_IOMEM > >> void __iomem *devm_ioremap_resource(struct device *dev, struct resource *res); > >> +#elif defined(CONFIG_COMPILE_TEST) > >> +static inline void __iomem *devm_ioremap_resource(struct device *dev, > >> + struct resource *res) > >> +{ > >> + pr_warn("no hardware io memory, only for COMPILE_TEST\n"); > >> + return (__force void __iomem *)ERR_PTR(-ENXIO); > >> +} > >> +#endif /* CONFIG_HAS_IOMEM || CONFIG_COMPILE_TEST */ > >> > >> /* allows to add/remove a custom action to devres stack */ > > > > To be honest, I think it's a bad idea to introduce wrappers functions > > that are only available when CONFIG_COMPILE_TEST is set. > > > > COMPILE_TEST is a great tool in general, but it has its limits. > > In particular, the case for !CONFIG_IOMEM is completely obscure > > and we won't find any bugs by allowing more drivers to be built > > in those configurations, but attempting to do it would cause > > endless churn by changing each instance of 'depends on HAS_IOMEM' > > to 'depends on HAS_IOMEM || COMPILE_TEST'. > > The point of this exercise is that we do not have to replace a good chunk of > 'depends on COMPILE_TEST' with 'depends on COMPILE_TEST && HAS_IOMEM' Ok, I see. > E.g. the typical Kconfig entry for your random SoC peripheral driver looks like > > config ARCH_FOOBAR_DRIVER > depends on ARCH_FOOBAR || COMPILE_TEST > ... > > Now when COMPILE_TEST is not set there is a implicit dependency on HAS_IOMEM > since the architecture will provide it. If COMPILE_TEST is selected the > driver will also be build-able on architectures that do no have HAS_IOMEM > and hence linking the driver fails. One way to fix this is of course to > replace the COMPILE_TEST with (COMPILE_TEST && HAS_IOMEM). But this is very > often overlooked and only noticed later on when somebody actually builds a > allyesconfig on an architecture that does not provide HAS_IOMEM. To avoid > these kinds of build errors and tedious fixup patches the idea is to provide > a stub function when HAS_IOMEM is not enabled, but COMPILE_TEST is enabled. AFAICT, NO_IOMEM only has a real purpose on UML these days. Could we take a shortcut here and make COMPILE_TEST depend on !UML? Getting random stuff to build on UML seems pointless to me and we special-case it in a number of places already. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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