linux-kernel - Re: [PATCH] staging: greybus/timesync: avoid divide by zero on X86 Qemu

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Date:   Tue, 27 Sep 2016 16:59:22 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Bryan O'Donoghue" <pure.logic@...us-software.ie>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        johan@...oldconsulting.com, Alex Elder <elder@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: greybus/timesync: avoid divide by zero on X86 Qemu

On Mon, Sep 26, 2016 at 10:31 PM, Bryan O'Donoghue
<pure.logic@...us-software.ie> wrote:
> A system configured without CONFIG_CPUFREQ will return 0 for cpufreq_get().
> greybus-timesync can subsequently then do a divide-by-zero as result. This
> patch fixes by checking for a zero return value from cpufreq_get() and
> setting to a default value of 19.2MHz.
>
> Reported-by: Rui Miguel Silva <rmfrfs@...il.com>
> Signed-off-by: Bryan O'Donoghue <pure.logic@...us-software.ie>
> ---
>  drivers/staging/greybus/timesync_platform.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/greybus/timesync_platform.c b/drivers/staging/greybus/timesync_platform.c
> index 50e8883..113f3d6 100644
> --- a/drivers/staging/greybus/timesync_platform.c
> +++ b/drivers/staging/greybus/timesync_platform.c
> @@ -20,6 +20,8 @@
>  #include "greybus.h"
>  #include "arche_platform.h"
>
> +#define DEFAULT_FRAMETIME_CLOCK_HZ 19200000
> +
>  static u32 gb_timesync_clock_frequency;
>  int (*arche_platform_change_state_cb)(enum arche_platform_state state,
>                                       struct gb_timesync_svc *pdata);
> @@ -32,8 +34,11 @@ u64 gb_timesync_platform_get_counter(void)
>
>  u32 gb_timesync_platform_get_clock_rate(void)
>  {
> -       if (unlikely(!gb_timesync_clock_frequency))
> -               return cpufreq_get(0);
> +       if (unlikely(!gb_timesync_clock_frequency)) {
> +               gb_timesync_clock_frequency = cpufreq_get(0);
> +               if (!gb_timesync_clock_frequency)
> +                       gb_timesync_clock_frequency = DEFAULT_FRAMETIME_CLOCK_HZ;
> +       }
>
>         return gb_timesync_clock_frequency;
>  }

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>