linux-kernel - Re: [PATCH] clocksource: fix clocksource_mmio_readX

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Date:	Tue, 22 Apr 2014 12:27:06 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Xiubo Li <Li.Xiubo@...escale.com>, tglx@...utronix.de
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clocksource: fix clocksource_mmio_readX_down

On 04/17/2014 11:27 AM, Xiubo Li wrote:
> For some clocksource devices, for example, the registers are 32-bit, while
> the lower 16-bit is used for timer counting(And reading the upper 16-bit
> will return 0).
>
> For example, when the counter value is 0x00001111, and then the
> ~readl_relaxed(to_mmio_clksrc(c)->reg) will return the value of 0xFFFFEEEE,
> but it should be 0x0000EEEE.
>
> So just using the c->mask to mask the unused bits.
>
> Signed-off-by: Xiubo Li <Li.Xiubo@...escale.com>
> ---
>   drivers/clocksource/mmio.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c
> index c0e2512..f17a0d1 100644
> --- a/drivers/clocksource/mmio.c
> +++ b/drivers/clocksource/mmio.c
> @@ -27,7 +27,7 @@ cycle_t clocksource_mmio_readl_up(struct clocksource *c)
>
>   cycle_t clocksource_mmio_readl_down(struct clocksource *c)
>   {
> -	return ~readl_relaxed(to_mmio_clksrc(c)->reg);
> +	return ~readl_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
>   }
>
>   cycle_t clocksource_mmio_readw_up(struct clocksource *c)
> @@ -37,7 +37,7 @@ cycle_t clocksource_mmio_readw_up(struct clocksource *c)
>
>   cycle_t clocksource_mmio_readw_down(struct clocksource *c)
>   {
> -	return ~(unsigned)readw_relaxed(to_mmio_clksrc(c)->reg);
> +	return ~(unsigned)readw_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
>   }
>
>   /**


Hi,

I realize there is some type confusion here:

cycle_t -> u64
readl_relaxed -> u32
readw_relaxed -> u16

and clocksource_mmio_readw_down returns a cast to unsigned (u32)

This patch makes sense but it obfuscate more the types in these 
functions. Worth to clarify the functions first ?


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