[PATCH] clocksource: mips-gic-timer: fix clocksource counter width

[PATCH] clocksource: mips-gic-timer: fix clocksource counter width

[Felix Fietkau]

This code needs to use ffs instead of fls on the mask to determine the
shift for reading the GIC_CONFIG_COUNTBITS field.

Fixes: e07127a077c7 ("clocksource: mips-gic-timer: Use new GIC accessor functions")
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 drivers/clocksource/mips-gic-timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
index a04808a21d4e..bf0eee78c6ef 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -166,7 +166,7 @@ static int __init __gic_clocksource_init(void)
 
 	/* Set clocksource mask. */
 	count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
-	count_width >>= __fls(GIC_CONFIG_COUNTBITS);
+	count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
 	count_width *= 4;
 	count_width += 32;
 	gic_clocksource.mask = CLOCKSOURCE_MASK(count_width);
-- 
2.14.2

Re: [PATCH] clocksource: mips-gic-timer: fix clocksource counter width

[Thomas Gleixner]

On Wed, 21 Feb 2018, Felix Fietkau wrote:

> This code needs to use ffs instead of fls on the mask to determine the
> shift for reading the GIC_CONFIG_COUNTBITS field.

Why?

Thanks,

	tglx
 
> Fixes: e07127a077c7 ("clocksource: mips-gic-timer: Use new GIC accessor functions")
> Cc: Paul Burton <paul.burton@imgtec.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>  drivers/clocksource/mips-gic-timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
> index a04808a21d4e..bf0eee78c6ef 100644
> --- a/drivers/clocksource/mips-gic-timer.c
> +++ b/drivers/clocksource/mips-gic-timer.c
> @@ -166,7 +166,7 @@ static int __init __gic_clocksource_init(void)
>  
>  	/* Set clocksource mask. */
>  	count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
> -	count_width >>= __fls(GIC_CONFIG_COUNTBITS);
> +	count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
>  	count_width *= 4;
>  	count_width += 32;
>  	gic_clocksource.mask = CLOCKSOURCE_MASK(count_width);
> -- 
> 2.14.2
> 
> 

Re: [PATCH] clocksource: mips-gic-timer: fix clocksource counter width

[Felix Fietkau]

On 2018-02-28 09:56, Thomas Gleixner wrote:
> On Wed, 21 Feb 2018, Felix Fietkau wrote:
> 
>> This code needs to use ffs instead of fls on the mask to determine the
>> shift for reading the GIC_CONFIG_COUNTBITS field.
> 
> Why?
>>  	count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
>> -	count_width >>= __fls(GIC_CONFIG_COUNTBITS);
>> +	count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
This code is trying to extract the GIC_CONFIG_COUNTBITS field from
read_gic_config(), so it needs to shift count_width right by the index
of the least significant bit (__ffs) instead of the most significant bit
(__fls) of the field mask.

- Felix

Re: [PATCH] clocksource: mips-gic-timer: fix clocksource counter width

[Thomas Gleixner]

On Wed, 28 Feb 2018, Felix Fietkau wrote:
> On 2018-02-28 09:56, Thomas Gleixner wrote:
> > On Wed, 21 Feb 2018, Felix Fietkau wrote:
> > 
> >> This code needs to use ffs instead of fls on the mask to determine the
> >> shift for reading the GIC_CONFIG_COUNTBITS field.
> > 
> > Why?
> >>  	count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
> >> -	count_width >>= __fls(GIC_CONFIG_COUNTBITS);
> >> +	count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
> This code is trying to extract the GIC_CONFIG_COUNTBITS field from
> read_gic_config(), so it needs to shift count_width right by the index
> of the least significant bit (__ffs) instead of the most significant bit
> (__fls) of the field mask.

Sure, but that information wants to be in the changelog.

Thanks,

	tglx