linux-kernel - Re: [PATCH] clocksource: Fix arm_arch_timer clockmode when vDSO disabled

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Message-ID: <a81251e813d54caddd56b9aac4b55e85@kernel.org>
Date:   Fri, 21 Feb 2020 13:34:06 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will.deacon@....com, linux@...linux.org.uk, luto@...nel.org,
        tglx@...utronix.de, m.szyprowski@...sung.com, mark.rutland@....com
Subject: Re: [PATCH] clocksource: Fix arm_arch_timer clockmode when vDSO
 disabled

Vincenzo,

Please include Mark and myself for anything that touches the arch timers
(get_maintainer.pl will tell you who you need to cc).

On 2020-02-21 13:03, Vincenzo Frascino wrote:
> The arm_arch_timer requires that VDSO_CLOCKMODE_ARCHTIMER to be
> defined to compile correctly. On arm the vDSO can be disabled and when
> this is the case the compilation ends prematurely with an error:
> 
>  $ make ARCH=arm multi_v7_defconfig
>  $ ./scripts/config -d VDSO
>  $ make
> 
> drivers/clocksource/arm_arch_timer.c:73:44: error:
> ‘VDSO_CLOCKMODE_ARCHTIMER’ undeclared here (not in a function)
>   static enum vdso_clock_mode vdso_default = VDSO_CLOCKMODE_ARCHTIMER;
>                                              ^
> scripts/Makefile.build:267: recipe for target
> 'drivers/clocksource/arm_arch_timer.o' failed
> make[2]: *** [drivers/clocksource/arm_arch_timer.o] Error 1
> make[2]: *** Waiting for unfinished jobs....
> scripts/Makefile.build:505: recipe for target 'drivers/clocksource' 
> failed
> make[1]: *** [drivers/clocksource] Error 2
> make[1]: *** Waiting for unfinished jobs....
> Makefile:1683: recipe for target 'drivers' failed
> make: *** [drivers] Error 2
> 
> Define VDSO_CLOCKMODE_ARCHTIMER as VDSO_CLOCKMODE_NONE when the vDSOs 
> are
> not enabled to address the issue.
> 
> Fixes: 5e3c6a312a09 ("ARM/arm64: vdso: Use common vdso clock mode 
> storage")
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c
> b/drivers/clocksource/arm_arch_timer.c
> index ee2420d56f67..619839221f94 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -49,6 +49,11 @@
>  #define CNTV_TVAL	0x38
>  #define CNTV_CTL	0x3c
> 
> +#ifndef CONFIG_GENERIC_GETTIMEOFDAY
> +/* The define below is required because on arm the VDSOs can be 
> disabled */
> +#define VDSO_CLOCKMODE_ARCHTIMER	VDSO_CLOCKMODE_NONE
> +#endif /* CONFIG_GENERIC_GETTIMEOFDAY */

This feels pretty clunky.

I'd extect VDSO_ARCH_CLOCKMODES (or some similar architecture-specific
symbol) to be used for vdso_default, and that symbol to be defined as
VDSO_CLOCKMODE_NONE when CONFIG_GENERIC_GETTIMEOFDAY isn't selected.

Otherwise, you'll end-up replicating the same pattern in every
clock-source that gets used by the VDSO.

         M.
-- 
Jazz is not dead. It just smells funny...