linux-kernel - Re: [PATCH v2 10/10] clocksource: import ARC timer driver

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Date:   Fri, 4 Nov 2016 00:01:46 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     Noam Camus <noamca@...lanox.com>, tglx@...utronix.de,
        linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Alexey.Brodkin@...opsys.com
Subject: Re: [PATCH v2 10/10] clocksource: import ARC timer driver

On Thu, Nov 03, 2016 at 03:50:21PM -0700, Vineet Gupta wrote:
> On 11/03/2016 03:38 PM, Daniel Lezcano wrote:
> > On Thu, Nov 03, 2016 at 02:31:41PM -0700, Vineet Gupta wrote:
> >> This adds support for
> >>
> >>  - CONFIG_ARC_TIMERS : legacy 32-bit TIMER0 and TIMER1 which count UP
> >>    from @CNT to @LIMIT, before optionally triggering an interrupt.
> >>    These are programmed using ARC auxiliary register interface.
> >>    These are present in all ARC cores (ARC700 and ARC HS38)
> >>    TIMER0 serves as clockevent for all ARC linux builds.
> >>    TIMER1 is used for clocksource in arc700 builds.
> >>
> >>  - CONFIG_ARC_TIMERS_64BIT: 64-bit counters, RTC and GFRC found in
> >>    ARC HS38 cores. These are independnet IP blocks with different
> >>    programming model respectively.
> >>
> >> Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> >> ---
> > 
> > [ ... ]
> > 
> >>  #include <linux/of_irq.h>
> >> -#include <asm/irq.h>
> >>  
> >>  #include <soc/arc/timers.h>
> >>  #include <soc/arc/mcip.h>
> >> @@ -263,7 +248,7 @@ static irqreturn_t timer_irq_handler(int irq, void *dev_id)
> >>  	 * irq_set_chip_and_handler() asked for handle_percpu_devid_irq()
> >>  	 */
> >>  	struct clock_event_device *evt = this_cpu_ptr(&arc_clockevent_device);
> >> -	int irq_reenable = clockevent_state_periodic(evt);
> >> +	int irq_reenable __maybe_unused = clockevent_state_periodic(evt);
> > 
> > Why is needed __maybe_unused ? I see in the previous driver 'irq_reenable' is
> > used or is there a change in the previous patches I missed ?
> 
> This is needed when not building for CONFIG_ARC (saw this when building for ARM)
> write_aux_reg() becomes a no-op which causes a warning:
> 
> 	write_aux_reg(ARC_REG_TIMER0_CTRL, irq_reenable | TIMER_CTRL_NH);

Instead of adding the __maybe_unused, changing in patch 7/10:

#define read_aux_reg(r) 0
#define write_aux_reg(r, v)

by

static inline int read_aux_reg(void *)
{
	return 0;
}

static inline void write_aux_reg(void *, u32)
{
	;
}

Should fix the warning.