linux-kernel - Re: [PATCH 2/2] pwm: Enable compile testing for some of drivers

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Message-ID: <20200107104234.wq74fska3szrg4ii@pengutronix.de>
Date:   Tue, 7 Jan 2020 11:42:34 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org,
        linux-riscv@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-tegra@...r.kernel.org, kernel@...gutronix.de,
        Richard Weinberger <richard@....at>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/2] pwm: Enable compile testing for some of drivers

Hello Krzysztof,

On Tue, Jan 07, 2020 at 09:25:39AM +0100, Krzysztof Kozlowski wrote:
> On Tue, Jan 07, 2020 at 08:26:45AM +0100, Uwe Kleine-König wrote:
> > On Mon, Dec 30, 2019 at 06:21:13PM +0100, Krzysztof Kozlowski wrote:
> > > Some of the PWM drivers can be compile tested to increase build
> > > coverage.
> > > 
> > > The Meson PWM driver requires COMMON_CLK dependency.
> > 
> > I'm surprised that there are not more that need this. Is HAVE_CLK not
> > enough?
> 
> Nope. E.g. for alpha architecture, HAVE_CLK is not set and without
> COMMON_CLK:
> 
> drivers/pwm/pwm-meson.o: In function `meson_pwm_init_channels':
> (.text+0x244): undefined reference to `devm_clk_register'

I see. devm_clk_register() only exists in include/linux/clk-provider.h.

> I guess other solution would be to add stubs for few clk functions...
> 
> > Also HAS_IOMEM is a typical requirement, but I tested with an ARCH=um
> > config (which does't have HAS_IOMEM) and they all compile fine.
> 
> Because of !HAS_IOMEM, since some time ARCH=um does not support
> COMPILE_TEST. Therefore HAS_IOMEM dependency is not needed for compile
> testing (and for regular build it is selected by ARCH).

Hehe, I didn't notice because for testing I just dropped the "depends on
..." lines in Kconfig instead of adding "|| COMPILE_TEST" :-) Still they
compile fine on UML.

Ah, since bc083a64b6c0 ("init/Kconfig: make COMPILE_TEST depend on
!UML") == v4.8-rc1~52^2~83 COMPILE_TEST cannot be enabled on UML, but
later 1bcbfbfdeb00 ("um: add dummy ioremap and iounmap functions")
== v4.13-rc1~8^2~6 UM got a dummy implementation. So maybe we could
revert bc083a64b6c0 today? (And if not, a comment about why near the
"depends on !UML" in init/Kconfig would be great.)

Orthogonal to that, I wonder if depending on HAS_IOMEM is right even
though the compile testers won't notice it missing. Or should HAS_IOMEM
be dropped?

> > > @@ -318,7 +319,7 @@ config PWM_MEDIATEK
> > >  
> > >  config PWM_MXS
> > >  	tristate "Freescale MXS PWM support"
> > > -	depends on ARCH_MXS && OF
> > > +	depends on (ARCH_MXS && OF) || COMPILE_TEST
> > >  	select STMP_DEVICE
> > >  	help
> > >  	  Generic PWM framework driver for Freescale MXS.
> > > @@ -328,7 +329,8 @@ config PWM_MXS
> > >  
> > >  config PWM_OMAP_DMTIMER
> > >  	tristate "OMAP Dual-Mode Timer PWM support"
> > > -	depends on OF && ARCH_OMAP && OMAP_DM_TIMER
> > > +	depends on (ARCH_OMAP && OMAP_DM_TIMER) || COMPILE_TEST
> > > +	depends on OF
> > 
> > I'm surprised that OF isn't required for PWM_MXS but is is for
> > PWM_OMAP_DMTIMER. pwm-mxs compiles without CONFIG_OF, didn't test
> > pwm-omap-dmtimer.
> 
> Since some time !OF has all necessary stubs so OF is actually needed
> only for binding, not compiling.

That doesn't explain why you handle PWM_MXS and PWM_OMAP_DMTIMER
differently though.

Best regards
Uwe

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