Re: [PATCH 6/9] clocksource: kona: fix get_counter error handling

[Ray Jui]

Hi Arnd,

On 8/10/2016 2:54 PM, Arnd Bergmann wrote:
> I could not figure out why, but gcc cannot prove that the
> kona_timer_init function always initializes its two outputs,
> and we get a warning for the use of the 'lsw' variable later,
> which is obviously correct.
>
> drivers/clocksource/bcm_kona_timer.c: In function 'kona_timer_init':
> drivers/clocksource/bcm_kona_timer.c:119:13: error: 'lsw' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> Slightly reordering the loop makes the warning disappear, after
> it becomes more obvious to the compiler that the loop is
> always entered on the first iteration.
>
> As pointed out by Ray Jui, there is a related problem in the
> way we deal with the loop running into the limit, as we just
> keep going there with an invalid counter data, so instead we
> now propagate a -ETIMEDOUT result to the caller.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> Link: https://patchwork.kernel.org/patch/9174261/
> ---
> Originally sent this as a warning fix only on June 13, this
> version actually fixes the incorrect data problem.
> ---
>  drivers/clocksource/bcm_kona_timer.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/clocksource/bcm_kona_timer.c b/drivers/clocksource/bcm_kona_timer.c
> index 7e3fd375a627..92f6e4deee74 100644
> --- a/drivers/clocksource/bcm_kona_timer.c
> +++ b/drivers/clocksource/bcm_kona_timer.c
> @@ -66,10 +66,10 @@ static void kona_timer_disable_and_clear(void __iomem *base)
>
>  }
>
> -static void
> +static int
>  kona_timer_get_counter(void __iomem *timer_base, uint32_t *msw, uint32_t *lsw)
>  {
> -	int loop_limit = 4;
> +	int loop_limit = 3;
>
>  	/*
>  	 * Read 64-bit free running counter
> @@ -83,18 +83,19 @@ kona_timer_get_counter(void __iomem *timer_base, uint32_t *msw, uint32_t *lsw)
>  	 *      if new hi-word is equal to previously read hi-word then stop.
>  	 */
>
> -	while (--loop_limit) {
> +	do {
>  		*msw = readl(timer_base + KONA_GPTIMER_STCHI_OFFSET);
>  		*lsw = readl(timer_base + KONA_GPTIMER_STCLO_OFFSET);
>  		if (*msw == readl(timer_base + KONA_GPTIMER_STCHI_OFFSET))
>  			break;
> -	}
> +	} while (--loop_limit);
>  	if (!loop_limit) {
>  		pr_err("bcm_kona_timer: getting counter failed.\n");
>  		pr_err(" Timer will be impacted\n");
> +		return -ETIMEDOUT;
>  	}
>
> -	return;
> +	return 0;
>  }
>
>  static int kona_timer_set_next_event(unsigned long clc,
> @@ -112,8 +113,11 @@ static int kona_timer_set_next_event(unsigned long clc,
>
>  	uint32_t lsw, msw;
>  	uint32_t reg;
> +	int ret;
>
> -	kona_timer_get_counter(timers.tmr_regs, &msw, &lsw);
> +	ret = kona_timer_get_counter(timers.tmr_regs, &msw, &lsw);
> +	if (ret)
> +		return ret;
>
>  	/* Load the "next" event tick value */
>  	writel(lsw + clc, timers.tmr_regs + KONA_GPTIMER_STCM0_OFFSET);

The change looks good to me! Thanks!

Acked-by: Ray Jui <ray.jui@xxxxxxxxxxxx>