linux-kernel - Re: [PATCH v2] clocksource/drivers/arm_global_timer: Simplify prescaler register access

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Date: Sat, 24 Feb 2024 22:55:19 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
 tglx@...utronix.de
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 patrice.chotard@...s.st.com, linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH v2] clocksource/drivers/arm_global_timer: Simplify
 prescaler register access

On 24/02/2024 22:35, Martin Blumenstingl wrote:
> Use GENMASK() to define the prescaler mask and make the whole driver use
> the mask (together with helpers such as FIELD_{GET,PREP,FIT}) instead of
> needing an additional shift and max value constant.
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> ---
> Changes from v1 at [0]:
> - use FIELD_FIT() to check whether psv overflows the register
> - update the description accordingly
> 
> 
> [0] https://lore.kernel.org/lkml/20240221214348.2299636-1-martin.blumenstingl@googlemail.com/
> 
> 
>   drivers/clocksource/arm_global_timer.c | 19 ++++++++-----------
>   1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
> index 8dd1e46b7176..49b094a20717 100644
> --- a/drivers/clocksource/arm_global_timer.c
> +++ b/drivers/clocksource/arm_global_timer.c
> @@ -9,6 +9,7 @@
>   
>   #include <linux/init.h>
>   #include <linux/interrupt.h>
> +#include <linux/bitfield.h>
>   #include <linux/clocksource.h>
>   #include <linux/clockchips.h>
>   #include <linux/cpu.h>
> @@ -31,10 +32,7 @@
>   #define GT_CONTROL_COMP_ENABLE		BIT(1)	/* banked */
>   #define GT_CONTROL_IRQ_ENABLE		BIT(2)	/* banked */
>   #define GT_CONTROL_AUTO_INC		BIT(3)	/* banked */
> -#define GT_CONTROL_PRESCALER_SHIFT      8
> -#define GT_CONTROL_PRESCALER_MAX        0xFF
> -#define GT_CONTROL_PRESCALER_MASK       (GT_CONTROL_PRESCALER_MAX << \
> -					 GT_CONTROL_PRESCALER_SHIFT)
> +#define GT_CONTROL_PRESCALER_MASK	GENMASK(15, 8)
>   
>   #define GT_INT_STATUS	0x0c
>   #define GT_INT_STATUS_EVENT_FLAG	BIT(0)
> @@ -247,7 +245,7 @@ static void gt_write_presc(u32 psv)
>   
>   	reg = readl(gt_base + GT_CONTROL);
>   	reg &= ~GT_CONTROL_PRESCALER_MASK;
> -	reg |= psv << GT_CONTROL_PRESCALER_SHIFT;
> +	reg |= FIELD_PREP(GT_CONTROL_PRESCALER_MASK, psv);
>   	writel(reg, gt_base + GT_CONTROL);
>   }
>   
> @@ -256,8 +254,7 @@ static u32 gt_read_presc(void)
>   	u32 reg;
>   
>   	reg = readl(gt_base + GT_CONTROL);
> -	reg &= GT_CONTROL_PRESCALER_MASK;
> -	return reg >> GT_CONTROL_PRESCALER_SHIFT;
> +	return FIELD_GET(GT_CONTROL_PRESCALER_MASK, reg);
>   }
>   
>   static void __init gt_delay_timer_init(void)
> @@ -272,9 +269,9 @@ static int __init gt_clocksource_init(void)
>   	writel(0, gt_base + GT_COUNTER0);
>   	writel(0, gt_base + GT_COUNTER1);
>   	/* set prescaler and enable timer on all the cores */
> -	writel(((CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) <<
> -		GT_CONTROL_PRESCALER_SHIFT)
> -	       | GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
> +	writel(FIELD_PREP(GT_CONTROL_PRESCALER_MASK,
> +			  CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) |
> +	       GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
>   
>   #ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
>   	sched_clock_register(gt_sched_clock_read, 64, gt_target_rate);
> @@ -301,7 +298,7 @@ static int gt_clk_rate_change_cb(struct notifier_block *nb,
>   		psv--;
>   
>   		/* prescaler within legal range? */
> -		if (psv < 0 || psv > GT_CONTROL_PRESCALER_MAX)
> +		if (psv < 0 || !FIELD_FIT(GT_CONTROL_PRESCALER_MASK, psv))
>   			return NOTIFY_BAD;

Won't FIELD_FIT cover psv < 0 also ?


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